The town of Sumner in Tallahatchie County served as the venue for the trial as the body had been found there. Sumner had only one boarding house and the small town was besieged by reporters from all over the country. David Halberstam called it "the first great media event of the civil rights movement". A reporter who had covered the trials of Bruno Hauptmann and Machine Gun Kelly remarked that this was the most publicity for any trial he had ever seen. No hotels were available for black visitors. Mamie Till Bradley arrived to testify and the trial also attracted black congressman Charles Diggs from Michigan. Bradley, Diggs, and several black reporters stayed at Howard's home in Mound Bayou. Located on a large lot and surrounded by Howard's armed guards, it resembled a compound. The day before the start of the trial, a young black man named Frank Young arrived to tell Howard he knew of two witnesses to the crime. Levi "Too Tight" Collins and Henry Lee Loggins were black employees of Leslie Milam, J. W.'s brother, in whose shed Till was beaten. Collins and Loggins were spotted with J. W. Milam, Bryant, and Till. The prosecution team was unaware of Collins and Loggins. Sheriff Strider, however, booked them into the Charleston, Mississippi jail to keep them from testifying.
The trial was held in September 1955, lasting for five days; and attendees remember the weather being very hot. The courtroom was filled to its 280-spectator capacity, and as a matter of course was racially segregated. Press from major national newspapers attended, including black publications; black reporters were made to sit segregated from the white press, farther from the jury. Sheriff Strider welcomed black spectators coming back from lunch with a cheerful, "Hello, Niggers!" Some visitors from the North found the court to be run with surprising informality. Jury members were allowed to drink beer on duty, and many white men in the audience wore handguns holstered to their belts.
The defense's primary strategy was arguing that the body pulled from the river could not be positively identified, and they questioned whether Till was dead at all. The defense asserted that Bryant and Milam had taken Till, but had let him go. They attempted to prove that Mose Wright—who was addressed as "Uncle Mose" by the prosecution and "Mose" by the defense—could not identify Bryant and Milam as the men who took Till from his cabin. Only Milam's flashlight was in use, and no other lights in the house were turned on. Milam and Bryant identified themselves to Wright the evening they took Till—the third man did not speak—but Wright only saw Milam clearly. Wright's testimony was considered remarkably courageous and a first in the state for a black man implicating the guilt of a white man in court.
Journalist James Hicks, who worked for the black news wire service National News Association, was present in the courtroom; he was especially impressed that Wright stood to identify Milam, pointing to him and saying "Thar he" (There he is),[note 7] calling it a historic moment and one filled with "electricity". A writer for the New York Post noted that following his identification, Wright sat "with a lurch which told better than anything else the cost in strength to him of the thing he had done". A reporter who covered the trial for the New Orleans Times-Picayune stated it was "the most dramatic thing I saw in my career".
Mamie Till Bradley testified that she instructed her son to watch his manners in Mississippi and that should a situation ever come to his being asked to get on his knees to ask forgiveness of a white person, he should do it without a thought. The defense questioned her identification of her son in the casket in Chicago and a $400 life insurance policy she had taken out on him.
While the trial progressed, Leflore County Sheriff George Smith, Howard, and several reporters, both black and white, attempted to locate Collins and Loggins. They could not, but found three witnesses who had seen Collins and Loggins with Milam and Bryant on Leslie Milam's property. Two of them testified that they heard someone being beaten, blows, and cries. One testified so quietly the judge ordered him several times to speak louder; he said he heard the victim call out, "Mama, Lord have mercy. Lord have mercy." Judge Curtis Swango allowed Carolyn Bryant to testify, but not in front of the jury, after the prosecution objected that her testimony was irrelevant to Till's abduction and murder. It may have been leaked in any case to the jury. Sheriff Strider testified for the defense his theory that Till was alive, the body retrieved from the river was white, and a doctor from Greenwood stated on the stand that the body was too decomposed to identify, and therefore had been in the water too long for it to be Till.
In the concluding statements, one prosecuting attorney admitted that what Till did was wrong, but it warranted a spanking, not murder. Gerald Chatham passionately called for justice and mocked the sheriff and doctor's statements that alluded to a conspiracy. Mamie Bradley indicated she was very impressed with his summation. The defense stated that the prosecution's theory of the events the night Till was murdered were improbable, and said the jury's "forefathers would turn over in their graves" if they convicted Bryant and Milam. Only three outcomes were possible in Mississippi for capital murder: life imprisonment, the death penalty, or acquittal. On September 23 the all-white jury acquitted both defendants after a 67-minute deliberation; one juror said, "If we hadn't stopped to drink pop, it wouldn't have taken that long."
In post-trial analyses, blame for the outcome varied. Mamie Till Bradley was criticized for not crying enough on the stand. The jury was noted to have been picked almost exclusively from the hill country section of Tallahatchie County, which, due to its poorer economic make-up, found whites and blacks competing for land and other agrarian opportunities. Unlike the population living closer to the river (and thus closer to Bryant and Milam in Leflore County). who possessed a noblesse oblige toward blacks according to historian Stephen Whitaker, those in the eastern part of the county were remarkably virulent in their racism. The prosecution was criticized for dismissing any potential juror who knew Milam or Bryant, for the fear that such a juror would vote to acquit. Afterward, Whitaker noted that this was a mistake as anyone who had personally known the defendants usually disliked them. One juror voted twice to convict, but on the third discussion, acquiesced and voted with the rest of the jury to acquit. In later interviews, the jurors acknowledged that they knew Bryant and Milam were guilty, but simply did not believe life imprisonment or the death penalty fit punishment for whites who had killed a black man. This is somewhat disputed by later interviews with two jurors who stated as late as 2005 that they believed the defense's case, that the prosecution had not proven that Till had died, and that it was his body that was removed from the river.
In November 1955, a grand jury declined to indict Bryant and Milam for kidnapping, despite the testimony given that they had admitted taking Till. Mose Wright and a young man named Willie Reed, who testified to seeing Milam enter the shed from which screams and blows were heard, both testified in front of the grand jury. T. R. M. Howard paid to relocate Wright, Reed, and another black witness who testified against Milam and Bryant, to Chicago. Reed, who later changed his name to Willie Louis to avoid being found, continued to live in the Chicago area until his death on July 18, 2013. He avoided publicity and kept his history secret from his wife until she was told by a relative. Reed began to speak publicly about the case in the PBS documentary The Murder of Emmett Till in 2003.