Katherine Mary Lyon (aged 10), and Sheila Mary Lyon (aged 12) were two sisters who disappeared without a trace during a trip to a local mall in the suburbs of Washington, D.C., in 1975. Known colloquially as The Lyon Sisters, their case resulted in one of the largest police investigations in Washington Metropolitan Area history. It is "one of the most high-profile unsolved cases in the D.C. area." The case remains unsolved.
The immense media attention given to this case at the time, its significance in the Washington area’s criminal history, and the fact that their disappearance has never been explained, has resulted in the story being revisited on a regular basis, and it has started to pass into the area’s folklore.
Background to the sisters' disappearance
The two sisters were born to John and Mary Lyon in Kensington, Maryland. They had an older brother, Jay, who later became a policeman. Their father was a well-known radio personality at WMAL, a local radio station then held by the owner of the ABC Television affiliate in Washington and the now-defunct Washington Star; he later worked as a victims counselor. Immediately following the girls' disappearance, the U.S. was pulling out of Vietnam, but their disappearance continued to be featured in high-profile stories on the media for months.
Located a half mile away from their home was Wheaton Plaza shopping mall (now Westfield Wheaton). On March 25, 1975, Katherine and Sheila Lyon were going to see the Easter exhibits. It was their spring vacation and they planned to have lunch at the Orange Bowl. They left home between 11:00 AM and noon. Their mother had instructed them to return home by 4:00 PM; when they had not arrived by 7:00 PM, the police were called and an extensive search was conducted. Police felt comfortable enough with accuracy of this timeline to release it to the public.
- 11:00 AM to noon: The girls leave home.
- 1:00 PM: A neighborhood child tells investigators that he saw both of the girls together outside the Orange Bowl. He also told the investigators that the sisters were speaking to an unidentified man.
- 2:00 PM: The girls' older brother saw them at the Orange Bowl eating pizza together.
- 2:30 to 3:00 PM: A friend sees the girls walking westward down a street near the mall which would have been one of the most direct routes from the mall to their home. This is the final sighting of the sisters that is absolutely confirmed by the police.
- 4:00 PM: This curfew set by their mother passes. The girls are expected home and do not arrive.
- 7:00 PM: Police are called. The investigation and an active search by professionals begins.
Police were told by witnesses that the sisters were in the Wheaton Plaza mall at approximately 1 PM. A neighborhood boy, who knew the sisters, reported that he saw them together outside the Orange Bowl speaking with an unidentified man, about 6 feet tall, 50 to 60 years old, and wearing a brown suit. The man was carrying a briefcase with a tape recorder inside; there were also other children around who were speaking into a microphone he was holding. The witness's description of the man led authorities to view the unknown person as a prime suspect in the Lyon sisters' case and two composite sketches of the man were created.
Police investigating the case followed up on reports from several people who said they recognized the sketch of the unknown man with the briefcase. Press reports indicated that a man matching the sketch was seen a few weeks earlier at the Marlow Heights Shopping Center and the Iverson Mall, both in neighboring Prince George's County, Maryland. These people reported that he had approached several young girls and asked them to read an answering machine message typed on an index card into his hand-held microphone. The police never publicly acknowledged a direct link between these reports and the Lyon sisters' disappearance.
As the weeks wore on, numerous volunteer groups combed vacant lots and stream beds for the sisters. The search continued and press interest reached such a fever pitch that on May 23, 1975, Maryland Lt. Gov. Blair Lee summoned 122 National Guardsmen to participate in a search of a Montgomery County forest for the missing girls.
No trace of the girls was ever found.
On April 7, 1975, about two weeks after their disappearance, a witness in Manassas, Virginia, reported seeing two girls resembling Sheila and Katherine in the rear of a beige 1968 Ford station wagon. The witness stated that the girls were bound and gagged in the vehicle. The driver of the station wagon resembled the man in the publicly available sketch of the prime suspect. The witness further claimed that when the driver spotted the witness tailing him, he ran a red light and sped west on Route 234 towards Interstate 66 in Virginia. The station wagon had Maryland license plates with the possible combination "DMT-6**." The last two numbers are unknown due to the bending of the car's plate. The known combination was issued in Cumberland, Hagerstown, and Baltimore, Maryland at the time. This supposed sighting inspired a small army of mobile citizen band (CB) radio users to scour the area throughout the evening and into the night with a running commentary and chatter but without any tangible results. A search for matching plate numbers failed to produce any information. Although this witness's report was at first treated as credible, and a media firestorm erupted because of it, it was later deemed "questionable" by police. Despite its questionable nature, media continue to mention this report as credible.
Several phone calls from people claiming to have the girls and offering to exchange them for ransom money were made to the Lyon family in the immediate aftermath of the sisters' disappearances. The one that went the furthest and that had seemed most credible began with an anonymous male voice on April 4, 1975, and demanded that John Lyon leave a briefcase with $10,000 inside an Annapolis, Maryland, courthouse restroom. The money was left just as the instructions from the caller required, but the money was never claimed. This same anonymous person called John Lyon later and maintained that police had surrounded the courthouse and he could not retrieve the ransom. The man was told that he would have to show some evidence of having the Lyon sisters in his custody before another attempt would be made to leave him a ransom. Although the caller then said he would be in touch with the family, he never contacted them again.
Fred Howard Coffey was convicted in 1987 for the 1979 beating, strangulation murder, and molestation of a 10-year-old girl in North Carolina and (as of 2012[update]) is serving a life sentence (after an earlier death sentence was overturned) in a North Carolina prison. Authorities learned that he interviewed for a job (and was subsequently employed) in Silver Spring, Maryland, six days after the Lyon sisters vanished. Silver Spring is a short distance from Wheaton Plaza. Investigators have been unable to determine if Coffey is connected to the case, and he has never been charged in the disappearances.
Raymond Rudolph Mileski Sr. was another possible suspect named in press reports. Mileski resided in Suitland, Maryland in 1975, not far from the malls in Prince George's County that had reported a man with a microphone approaching young girls. In a family disagreement, Mileski murdered his wife and teenage son and wounded another son inside their home in November 1977. He was convicted of the homicides and sentenced to 40 years in prison. Based on both prison informants tips and Mileski’s own claims to know something about the Lyon sisters case, which he offered to share more fully in exchange for more favorable prison conditions, authorities searched his former residence in April 1982, but no evidence was discovered. Mileski died in prison in 2004.
In February 2014, inmate Lloyd Welch was named as a "person of interest" in the case. Police said Welch, who was 18 years old at the time, and had since been convicted of rapes in three other states, had been "seen 'paying attention' to the sisters." 
- Cold case
- List of people who disappeared mysteriously
- John Brennan Crutchley, a deceased rapist and possible serial killer suspected of links to as many as 20 or so disappearances of teenaged girls and young women in and around the Washington, DC area.
- Justin Jouvenal; Dan Morse (11 February 2014). "Inmate Lloyd Welch named as ‘person of interest’ in 1975 Lyon sisters case". The Washington Post. Retrieved 11 February 2014.
-  Neal J. Conway blog
- "Md. Guardsmen to Join Hunt for Lyon Sisters". Pqasb.pqarchiver.com. 1975-05-23. Retrieved 2012-07-06.
- Personal Experience
- "Sheila Mary Lyon". The Charley Project. Retrieved 2012-07-06.
- "The Murder of Kathy Lynn Beatty [Archive] - Websleuths Crime Sleuthing Community". Websleuths.com. Retrieved 2012-07-06.
- Websleuth forum on Lyon Sisters (opinion forums but many newspaper articles and links are reprinted partially or in their entirety)
- Montgomery County Gazette Newspaper Article on the 30th Anniversary on impact on the community
- Missing person's profile of Sheila Lyon
- Missing person's profile of Katherine Lyon