But a lawyer for defendant Trent Mays said his 17-year-old client "did not rape the young lady in question."
Special Prosecutor Marianne Hemmeter and Mays' attorney, Brian Duncan, spoke at the opening of the juvenile court trial, which has drawn international attention to a small town in a football-loving region of eastern Ohio.
Hemmeter told Judge Thomas Lipps, who is hearing the case without a jury, that she would show that the girl was "somebody who was too impaired to say no, somebody who was too impaired to say stop."
The attorney for Mays' co-defendant, Ma'Lik Richmond, 16, gave no opening statement.
The case has divided the community amid allegations that more students should have been charged. It also has led to questions about the influence of the local football team, a source of a pride in a community that suffered massive job losses with the collapse of the steel industry.
Richmond and Mays are charged with digitally penetrating the West Virginia girl, first in the back seat of a moving car after a party Aug. 11 and then in the basement of a house. Mays also is charged with illegal use of a minor in nudity-oriented material.
Witnesses said the girl was so drunk she threw up at least twice and had trouble walking and speaking. She also was photographed being carried by the two boys.
In an excerpt of a videotaped interview with ABC's "20/20," Richmond said the photo was a joke. He contends the girl was awake and was a willing participant, the show said.
Following opening statements, prosecutors presented two witnesses, 17-year-old girls who saw the girl the night of the party. Questions by prosecutors and defence lawyers focused on how much the girl had been drinking that night.
One of the 17-year-old girls, a Steubenville High School student, said the 16-year-old girl was having trouble walking but never appeared to pass out. The other 17-year-old girl said she had never seen her friend so intoxicated.
If convicted, Mays and Richmond, who deny any wrongdoing, could be held in a juvenile jail until they turn 21.
The Associated Press normally does not identify minors charged in juvenile court, but Mays and Richmond have been widely identified in news coverage, and their names have been used in open court.
They were charged 10 days after the party, after a flurry of social media postings about the alleged attack led the girl and her family to go to police.
Steubenville officials have protested that outsiders have unfairly criticized police handling of the case and have given Steubenville a black eye. Officials created a website to counter misinformation about the case, disputing, for example, the allegation that the police department is full of ex-football players from the local powerhouse team, nicknamed Big Red.
Hacker activists have publicized tweets and other social media postings made the night of the alleged rape, including a 12-minute video in which one student joked about it while others in the background chimed in.
The National Organization of Women has demanded that the student be charged under the state's failure to report law. Attorney General Mike DeWine has called the video disgusting but said the student didn't have firsthand knowledge of the alleged assaults.
Bob Fitzsimmons, a lawyer for the girl's family, said, "The family wants this matter over so they can move on with their lives and their daughter's healing."
Dozens of witnesses for both sides were expected to testify at the trial. Their testimony is considered crucial because the girl was severely intoxicated that night and appeared to be passed out at times, according to several witnesses.
Associated Press writers Kantele Franko in Columbus and Vicki Smith in Morgantown, W.Va., contributed to this report.Suggest a correction