Teen testifies he witnessed sex assault of Ohio girl A witness testifies to alleged sex abuse The teenager testifies he took video of the incident with his phone The teen agreed to testify only after the judge granted him immunity Two other Steubenville teens are being tried on rape accusations Editor's note: Please note this story contains graphic language. (CNN) -- A teenager testified Friday that he saw one of the two Steubenville, Ohio, boys accused of raping a 16-year-old girl engage in sexual conduct with the girl during a car ride. The 17-year-old also told Judge Thomas Lipps that he used his cellphone to record Trent Mays putting his fingers inside the girl's vagina during a drive from one party to another. The boy said he deleted the video the next morning. The teen, whom CNN is not identifying because of his age, testified only after Lipps, who is presiding over the trial without a jury, granted him immunity from prosecution. Mays, 17, and Ma'lik Richmond, 16, are accused of raping the girl during a series of end-of-summer parties in August. Trial focuses on text messages Mays also is accused of illegal use of a minor in nudity oriented material. Lawyers for the teens, both players on Steubenville's high school football team, say the two are innocent. CNN is not identifying the girl in line with its policy of not identifying the alleged victims of sexual assault. CNN also is not identifying minors who testify at the trial but is identifying Mays and Richmond, whose names have been used by court officials and their attorneys and in multiple media accounts. On Thursday, prosecutors presented texts messages they said were between Mays and various friends in which Mays allegedly discussed the girl's inebriation and acknowledged sexual conduct with her. Some of the messages were between Mays and the alleged victim. In one message she asks what happened "last night." And don't lie about anything. I need to know the truth. People keep asking. Idk (I don't know) what to say," the message said, according to Joann Gibb, a computer forensic investigator with the Ohio Bureau of Criminal Investigation, who read the messages to the court. Mays responded that "nothing happened last night," but told her in the message she performed a sex act on him, Gibb testified. In some of the messages from Mays, according to Gibb, he writes that he had sex with the girl. In others, he says the girl performed a sex act on him. One message asked Mays: " Did u do it?" He responded, according to Gibb: "No, lol. She could barely move. Another message to Mays from still another friend asked "how dead is she?" Mays responded, according to Gibb, "not at all, she's looking for her phone." Still another graphic message from Mays to a friend appeared to detail his anger over being accused of rape. I'm pissed all I got was a hand job, though. I should have raped since everyone thinks I did," the message said, according to Gibb. Prosecutors contend the text messages between Mays and his friends and classmates on August 12 detail a night of heavy drinking and the sexual abuse of the girl. The defense questioned the validity of the messages, with Mays' attorney asking computer forensic expert Gibb whether she could be absolutely sure the messages were from his client. "I can't put a person behind a cellphone," she said. In earlier testimony, teens who attended some of the booze-soaked parties testified the girl appeared to be drunk, stumbling and slurring words. Teens treated girl 'like a toy,' prosecutor says But on cross-examination some said she seemed to be able to walk and answer questions. Defense lawyers tried to dismantle what prosecutors said was the central argument in the case -- whether the girl was too drunk to understand what was happening to her. The trial, which is likely to stretch into the weekend, is moving quickly to accommodate the schedule of the judge.