Detective Josie Sutton (Sarah Brown) (Season 3) is a second generation cop, her father having been killed in a line of duty when she was a child. She joined the squad at the start of the third season, following rumors of an affair with her sergeant at another precinct (rumors which proved to be false). This incident left her with something of a reputation which led to a less than warm welcome when she arrived, particularly from Vera. She tended to be hard on witnesses and suspects more often than the other detectives. Her time with the squad was no more than a few months, after which she took a personal leave and then apparently transferred out. This may have been caused by Scotty's advances, and her discomfort after the scandal with her former sergeant.
Detective Lennie Desalle (Sonya Leslie) (Season 2) was the second female homicide detective in Philadelphia, after Lilly Rush. She joined the squad in the spring of 2005. She was called to the scene when the skulls of nine women were found buried in the back yard of a house formerly owned by Simone Marks (Episode: "The Woods"). Lennie was part of the investigation into the murder of Simone, who was killed in the house in 1972, as well as the manhunt for George, who was still at large. After George was killed in a stand-off with Lilly, Lennie took down the pictures and information that the detectives had posted on George's victims. In the episode "Torn", Lilly said there were two female Homicide detectives (herself and Miller), suggesting Lennie was no longer in Homicide at that point.
Christina Rush (Nicki Aycox) (Seasons 2, 7) is Lilly's rebellious and irresponsible younger sister, who has long had a difficult relationship with Lilly. Christina becomes involved with Lilly's partner Scotty Valens against Lilly's wishes. Lilly still shows concern for her sister but is often frustrated by Christina's irresponsible behavior. It is revealed that the Christina ruined her relationship with Lilly when she slept with her fiance, Patrick. Something she tells Scotty very vaguely but still upsets Lilly to even hear him brought up. After Scotty learned she was linked to a credit card scam, Christina abruptly left without saying goodbye to him or Lilly and did not return until Season 7. She wanted Lily to co-sign a home rental agreement, but Lilly refused because she didn't trust her sister. Christina was revealed to be involved with a prescription drug fraud ring, and the leader of the ring was the father of her baby daughter. He later abducted her on suspicion she was informing Lilly about the group (she wasn't) but Lilly rescued her and her daughter and took down the ring's leader and his sidekick.
Ellen Rush (Meredith Baxter) (Seasons 3-4) is Lilly and Christina's alcoholic mother, who raised her children on welfare and often neglected them due to her drinking and promiscuity. She was first seen apparently sober in Season Three when she asked Lilly to be her Maid of Honor as she was getting married - for the fourth time. One year later, her husband had left her and Lilly was left to bail her out of jail after a particularly bad bender and then take care of her after she was diagnosed with cirrhosis of the liver due to years of alcohol abuse. Despite all this, Lilly and her mom bonded during what little time they had together before Ellen's sudden death in the Season Four finale.
Paul Cooper (Raymond J. Barry) (Seasons 6-7) is Lilly's father, who left the family when Lilly was six because of a toxic relationship with Lilly's mother and probably her drinking habit. He remarried to a woman named Celeste and relocated to Haddonfield, New Jersey, where he was an avid chess player. He and Celeste had two children, Maggie and Finn. Lilly only reconnected with Paul in season six (episode 06.11, "Wings"), though the two discussed several letters Paul sent to Lilly when she was sixteen. Paul carried a lot of guilt for leaving her, though he believed leaving her mother was the right thing to do because "some people just shouldn't stay together." In a letter to his daughter Paul admitted that he, like his ex-wife, was an alcoholic. Lilly agreed to meet Paul's family - her stepmother and half-siblings - but used work as an excuse to get out of it several times, whether she was actually working or not. When she finally did join the family for dinner, Celeste made it clear that she wanted Lilly and Paul to stop all the drama because, no matter how they all came together, they were family. Neither Paul nor Lilly brought up Christina in conversation, implying he was not Christina's father. In episode 07.21, "Almost Paradise", Lilly entered Paul's home to find Christina in the kitchen with him. Lilly stormed out but later met with Christina at a diner. Whether Paul is Christina's father or not, the two rarely talk.
Finn Cooper (Brett Davern) (Season 7) is Paul's teenage son and Lilly's half-brother. Sometime after learning of Lilly's existence, he got himself arrested on a drunk and disorderly conduct charge in order to be taken to where she worked. Lilly told him there were easier ways if he wanted to see her and the two apparently began meeting soon after, with Lilly telling him more about their father's past. Months later, Finn stole Paul's car and ran away to Atlantic City after the two had an argument. Lilly would later help Paul find Finn, at which point Finn announced his intention to become a cop like her, rather than going to college.
Moe Kitchener (Daniel Baldwin) (Seasons 6-7) was an instructor at the Pennsylvania Military Institute in 2005, when female student Kate Butler was murdered by a fellow cadet. Moe assisted in covering up the crime by burying her body in Philly. When her remains were found four years later, Moe again tried to cover up the crime by running Lilly's car off a bridge. Lilly survived, however, and Moe was arrested. Lilly was later outraged when Moe was granted bail shortly thereafter, and began to wage a campaign of retaliation against Moe. Using her influence as a cop, she prevented him from obtaining a loan after he was dismissed from P.M.I., she had traffic officers place a boot on his car, and arranged to have him arrested on a DUI charge. Moe was later found dead in his car from a gunshot to the head. Lilly was questioned about the murder until Hank Butler, Kate's father, confessed to shooting Moe for his role in covering up his daughter's murder.
Deputy Commissioner Pat Doherty (Keith Szarabajka) (Seasons 6-7) is A high-ranking, political-minded police officer in the pocket of corrupt city councilman Grover Boone. Doherty freely admitted to never liking Stillman, but it wasn't until Stillman questioned Boone about the murder of a man who'd run against him, that Stillman truly earned Doherty's enmity. Doherty retaliated by having his former driver (now an officer in Internal Affairs) follow Jeffries to investigate evidence of Jeffries accepting bribes. Stillman learned of this investigation after Jeffries was shot, but later presented evidence to Doherty that cleared his name. He also warned Doherty, that he would "beat the ever-loving crap" out of Doherty, should he ever make trouble for someone under Stillman's command again. Months later Homcide was placed under Doherty's authority, bringing it, and Stillman, even further under his scruitny. In Jurisprudence, Doherty ordered Stillman to back off an off-the-books investigation into the death of a teenager held in dormitory for fear of department fallout. Because Stillman refused to back down, Doherty pulled rank and forced a transfer on Detective Kat Miller removing Miller from Stillman's unit. Stillman managed to pull some strings with of the Department brass and get Miller reinstated to Homicide a few weeks later, however. It is later revealed that Doherty's dislike of Stillman was based on having arrested Doherty's son Matt on a drug charge years earlier. After Matt reformed, got married and became a father, Doherty acknowledged that the arrest had changed his son for the better, and eased up on Stillman. Sadly, months later, Matt was found to be an accessory to the death of a young woman in the Badlands in 1993, and that Doherty, fearing his son may have been involved, had suppressed evidence. Matt later confessed while Doherty was forced to answer for his actions to his superiors. What punishment he faced is unclear.
Joseph Shaw (Kenny Johnson) (Seasons 3-4) is a counselor who worked with troubled youths, an attempt was made on his life just before he was about to testify after he witnessed a murder. After he was presumed dead, Joseph went into hiding until Lilly discovered him alive a year later. The two began a relationship, though it was hindered by Lilly's trust issues (as well as the return of her ex, Ray Williams, into her life). Joseph eventually realized Lilly couldn't love him the way he loved her and ended their relationship.
Ray Williams (Brennan Elliott) (Season 4) is a biker who had been involved with Lilly in the past, even having asked her to marry him at one point. He re-entered her life twice on the show, once while she was dating Joseph, which led to some friction between the two. When last seen, he told her he was leaving for California.
Dr. Frannie Ching (Susan Chuang) (Seasons 1-4) is a medical examiner who helped the squad in some cases. She joins to the crime lab replacing Dr. Barnsley. Although the victims have died several years ago, she is able to examine the dead bodies and find new evidence. In the episode "Baby Blues", she asked for the detectives to reopen the case of Iris Felice.
Louie Amante (Doug Spinuzza) (Seasons 1, 4-5, 7) is a CSI who usually works with the squad on cases involving fire or explosives. Several of the squad attended Louie's wedding in 2010, where they investigated the mysterious death of the bride's former fiancee two years earlier. Suspicion passed between the bride, members of her family, and even Louie himself, before the death was found to be a suicide.
ADA Jason Kite (Josh Hopkins) (Seasons 1-2, 3) is a persistent Assistant DA who was involved in a short-lived relationship with Lilly in the first season, which ended after he realized he would always come second to her job. He only appeared in one more episode after breaking it off with her. After a few drinks in the third season, Lilly left a message on Kite's voice-mail taking responsibility for the failure of their relationship.
ADA Alexandra Thomas (Bonnie Root) (Seasons 4-5) is an assistant DA who worked with the squad. She first came to their attention when she prosecuted a pedophile whose victims had included Scotty's brother. She and Scotty have clashed several times, largely due to Thomas being concerned with "the big picture" whereas Scotty is more concerned with individual victims. There had been hints of sexual tension between the two for some time, however, finally culminating in the two having an affair during the fifth season. Their relationship took a turn for the worse when her office disclosed that a serial bomber's intended target had survived, which led to another bomb which nearly killed the man's wife and daughter. Scotty blamed Thomas for this and she hasn't been seen on the show since. Given that Scotty started dating Frankie Lafferty months later, it's safe to say her relationship with Scotty is over.
ADA Curtis Bell (Jonathan LaPaglia) (Seasons 6-7) is an assistant DA who first assisted the squad with the murder of a promising politician. Bell often appears disorganized and forgetful, leading both detectives and suspects to underestimate him, until he surprises them with effective and timely information. In episode 6.15 "Witness Protection", he gives Miller very important information that helps to solve the case. In episode 6.17 "Officer Down", we learn his dad was a cop who was killed in the line of duty and in episode 6.18 "Mind Games", we learn he has a daughter and a difficult relationship with his ex-wife. In the sixth season finale, he asks Miller out and she accepts. The two begin a quiet relationship over the next several months. Bell is a single father of a young daughter and has had some custody issues with his ex (whom he refers to as "the soul-crusher"). Bell tends to socialize with the squad far more than Kite or Thomas did. His relationship with Miller deteriorates for a time due to their differing views on Miller's own custody battle with her ex, but they eventually reconcile.
Frankie Rafferty (Tania Raymonde) (Season 6) is a lab technician who works in the identification unit and begins flirting with Scotty when he stops by one day regarding a case. The two quickly start dating, however Frankie never tells Scotty she is married. Her husband Billy, from whom she is separated, finds out about Scotty and leaves harassing phone calls and even vandalizes his car, not knowing Scotty is a cop. Though Scotty is understandably upset with Frankie for not telling him about Billy, the two start to get past it, until Frankie decides to try and work things out with her husband, instead. Frankie and Billy eventually divorce, but Scotty is reluctant to try again with Frankie, suggesting things between them may be over for good.
Detective Eddie Saccardo (Bobby Cannavale) (Seasons 5-6, 7) is an uncouth but effective cop working Undercover, Saccardo first assisted the squad in investigating the murder of a reformed ex-convict. The rest of the squad grew to like Eddie, with the exception of Lilly, who seemed put off at every turn. Tensions eased slightly between the two of them weeks later, however, when they worked together to find a young woman's lost son. They later began dating for a few episodes, until he had to leave for a long term assignment. He met up with Lilly the following year while still undercover and the two rekindled their relationship. His undercover work meant any type of long-term relationship was impossible, however, and Lilly would be drawn towards FBI agent Ryan Cavanaugh months later. However, not much came from her attraction towards Ryan, but neither he nor Eddie are mentioned again near the series finale.
Detective Gil Sherman (Kevin McCorkle) (Seasons 1, 2, 3) is the Head of the Fugitive Squad. Formerly worked Homicide with Lt. Stillman. After hiding years of alcoholism through the late 1980s to mid 1990s, he left Homicide to enter rehab. Sherman shows up when a fugitive case intersects with a cold case investigation or to provide information on a case he previously worked on.
Detective Anna Mayes (Robin Weigert) (Seasons 1, 2, 3) is an old friend and colleague of Scotty's from West Detectives, Anna has assisted the squad on a few cases. She also had to deliver the bad news when the body of Elisa, Scotty's girlfriend, was found in the Schuylkill River.
Detective Pierson (James Hanlon) (Season 7) is a detective investigating the assault of several women in the seventh season. When evidence suggested Scotty's mother (see below) was one of the victims, Pierson quietly provided Scotty with information on the case.
Toni Halstead (Sonja Sohn) (Season 4-5) is an African-American nurse and single mother of teenage Andre, both of whom are neighbors to Vera. Their paths first crossed in a dispute over the noise from Andre's playing basketball outside Vera's apartment. After making peace, Vera began dating Toni and started to become a father figure to Andre. Toni broke things off after Vera's long working hours left little time for Andre, but a chance encounter led to the two of them rekindling their relationship. A later episode suggested Vera has since been cutting back on his long working hours to spend more time with them. Toni was not seen again after she and Vera reconciled. A later episode established that although she eventually moved in with Vera, things didn't work out and Vera eventually had to find a new place to live.
Andre Halstead (Oren Williams) (Season 4) is Toni Halstead's son who first meet Nick Vera when he was playing basketball outside Vera's apartment.
Elisa (Marisol Nichols) (Season 1) was Scotty's girlfriend during the first and early second season. She had some emotional problems and eventually died in an apparent suicide. Scotty refused to believe it was a suicide at first, jumping on any alternate explanation, however unlikely, but Elisa's suicide appears to have been just that.
Mike Valens (Nestor Carbonell) (Season 4) is Scotty's older brother, he was sexually assaulted by a coach as a child. He initially denied the incident had occurred but eventually, after a bout of depression, agreed to testify against the coach when Scotty convinced him to do so. Young Mike was played by Lorenzo James Henrie.
Ramiro Valens (Ismael 'East' Carlo) (Season 7) is Scotty's father. He approached his son for help after Rosa was injured in a purse-snatching.
Rosa Valens (Terri Hoyos) (Season 7) is Scotty's mother who was victim of a robbery but eventually speaking with another victim confirms Scotty's suspicions that his mother was the victim of a serial rapist, who was caught and arrested by Scotty soon after.
Lindsey Dunlay (Bahni Turpin) (Season 1, 3) is social worker specializing in children and a friend of Lilly's since high school. She has twice asked the squad to help troubled teenagers by investigating the murders of their parents. She later returned to take custody of an abandoned baby found in the squad.
Ryan Cavanaugh (Johnny Messner) (Season 7) is an FBI Agent who helped Lilly to identify the serial killer Paul Shepard. After having caught Sam, Ryan helped Lilly with another case (Ep. "Free Love").
Diane Yates (Susanna Thompson) (Season 7) is another FBI and former PPD cop. In 1980, she was in the drive-in with her boyfriend Barry Jensen when he was shot. Diane goes to Philadelphia because her mother has a stroke. Stillman keeps her company at the hospital and comforts her when she passes away.
George Marks (John Billingsley) (Season 2) was a serial killer of hideous intelligence, George was one of the few killers on the show to outwit Lilly and the squad, getting away with several murders over several years. Already troubled even as a child, his deranged mother, who suffered from hysterical blindness allowed a rapist to sexually assault him to save herself during a home invasion. Immediately after, George's mother became his first victim, using the gun the rapist knocked out of George's mother's hands. As an adult, George would cultivate a twisted obsession with strong women, using his position as a filing clerk with the Philadelphia Police Department to find examples of them in police reports (i.e. women who had been assaulted but had fought back against their attackers). Disguising himself as a cop, George would take these women into the woods, force them to strip down to their underwear, then proceed to hunt them using a pair of night vision goggles (much in the style of actual serial killer Robert Hansen) and an Arisaka Model 38 rifle. He would collect their heads as trophies, burying their bodies in the woods and burying the heads in the backyard of his childhood home. He would also fit the eye sockets of the skulls with black glass deer eyes, presumably as a gesture to make his victims see what was done to him in the house. Though the squad quickly recognized George as being responsible for the murders, they were unable to get him to confess, or find enough evidence to convict him. Instead, he merely taunted them with personal information he had read from their police files, before walking away unpunished. During the interrogation, however, George developed a fixation with Lilly and, months later, would lure her to his home. It was here that he forced her to relive the assault that she experienced as a child, when her alcoholic mother forced her to go out into the night to buy alcohol for her whereupon along the way she was attacked and robbed. She then broke him down when she stripped away his god complex to show that in the woods he was still "a little boy whose mother didn't love him". It was then that both realised they were somewhat both cut from the same cloth, with George knowing he had found a worthy executioner as he pulled a gun on her and demanded she shoot him or else he would shoot her. A tense standoff would end with Lilly firing upon George, shooting him three times in the chest, killing him instantly. The entire ordeal would still haunt her months later.