On May 24, 1913, a murder indictment was returned against Frank by a grand jury. The trial itself began on July 28. The windows were left open because of the heat, and in addition to the hundreds of spectators inside, a crowd gathered outside to watch the trial through the windows, a circumstance that may have contributed to witness and jury intimidation.
The prosecutor was Hugh M. Dorsey, who had recently tried and failed to obtain a conviction in two high profile murder cases--a third courtroom reverse could conceivably have meant the end of his career. Frank was represented by eight lawyers (some of them jury selection specialists), led by Luther Rosser. The prosecution's theory was that Conley's last affidavit was true, Frank was the murderer, and the murder notes had been dictated by Frank in an effort to pin the crime on Lee. The defense's theory was that Conley was the murderer, and that Lee helped Conley write the notes. The defense brought numerous witnesses who attested to Frank's alibi, which did not leave him enough time to have committed the crime. 
Conley reiterated his testimony from his final affidavit. He added to it by describing Frank as regularly having sex with women in his upstairs office on Saturdays while Conley kept a lookout. Another witness who, like Conley, had a criminal record, corroborated Conley. Although Conley admitted that he had changed his story and lied repeatedly, this did not damage the prosecution's case as much as might have been expected. Conley admitted to being an accessory, so it wasn't surprising that he had lied at first. Also, many white observers did not believe that a black man could have been intelligent enough to make up such a complicated story. 
The Georgian wrote, "Many people are arguing to themselves that the negro, no matter how hard he tried or how generously he was coached, still never could have framed up a story like the one he told unless there was some foundation in fact." Defense witnesses testified that there were too many people in the factory on Saturdays for Frank to have had trysts there. They pointed out that the windows of Frank's office lacked curtains. A large number of female factory workers testified for the defense of Frank's good character when it came to women. 
Frank spoke on his own behalf, by making an unsworn statement as allowed by Georgia Code, Section 1036; it did not permit any cross-examination without his consent and thus none occurred. Most of his four-hour speech consisted of an extremely long and detailed analysis of the accounting work he had done the day of Phagan's murder, meant to show that the act was too time-consuming for him to have committed the murder.  He ended with a description of how he viewed the crime, including an effective, and by some accounts moving, explanation of his nervousness:
Gentlemen, I was nervous. I was completely unstrung. Imagine yourself called from sound slumber in the early hours of the morning ... To see that little girl on the dawn of womanhood so cruelly murdered — it was a scene that would have melted stone. 
In its closing statements, the defense attempted to divert suspicion from Frank to Conley. Lead defense attorney Luther Rosser, said to the jury: "Who is Conley? He is a dirty, filthy, black, drunken, lying, nigger." Frank himself had issued a widely publicized statement questioning how the "perjured vaporizings of a black brute" could be accepted in testimony against him.
The prosecutor compared Frank to Dr. Jekyll and Mr. Hyde. He said that Frank had killed Phagan to keep her from talking. With the sensational coverage, public sentiment in Atlanta turned strongly against Frank. The defense requested a mistrial because it felt the jurors had been intimidated, but the motion was denied. In case of an acquittal, the judge feared for the safety of Frank and his lawyers, so he brokered a deal in which they would not be present when the verdict was read. On August 25, Frank was convicted of murder. The Constitution described the scene as Dorsey emerged from the steps of city hall: "The solicitor reached no farther than the sidewalk. While mounted men rode like Cossacks through the human swarm, three muscular men slung Mr. Dorsey on their shoulders and passed him over the heads of the crowd across the street."
- 'The Trial of Leo Frank: An Account'.
- Knight, Albert H. The Life of the Law. 1996, p. 1996.
- Dinnerstein, page 8.
- Levy, Eugene . "Is the Jew a White Man?" in Maurianne, Adams and John H. Bracey. Strangers & Neighbors: Relations Between Blacks & Jews in the United States. University of Massachusetts Press, 2000, pp. 261–270.
- "The Leo Frank Trial: A Chronology", compiled by Douglas O. Linder, University of Missouri-Kansas City School of Law.
- The New York Times, December 14, 1914.