David Stockwell, a forensics supervisor for the Contra Costa County Sheriff's Office, also said he found semen from at least one other person who is not among the seven defendants charged in the case.
He also found non-semen DNA from several of the defendants on evidence collected at the scene, Stockwell said.
The alleged rape happened on Oct. 24, 2009, during the school's homecoming dance.
The victim, a 16-year-old student, had gone to the dance but left early. She allegedly told a nurse the following day that she had been about to call her father to have him come pick her up when a boy she knew from her class, 16-year-old Cody Smith, invited her over to a courtyard area on the north side of campus to drink alcohol with him and his friends.
The victim told the nurse that she remembered drinking brandy with the group, but then got dizzy and blacked out. She woke up the next day in the hospital.
After she blacked out, a large group of males reportedly beat her, robbed her and sexually assaulted her while others stood by and watched, police said.
By the time police found the victim shortly before midnight, she was in a coma and nearly dead, Jim Carpenter, a pediatric consultant for the county's sexual assault response team, testified last week.
According to Carpenter, the victim had suffered multiple severe head injuries that caused swelling in her brain. She also had numerous other injuries all over her body. She was hypothermic and had a blood alcohol level of .355 percent.
Manuel Ortega, a 20-year-old Richmond resident, was arrested while he was fleeing from the scene, police said. According to Stockwell, Ortega's semen was found on the victim's body, and the victim's DNA was found on Ortega's body.
Several investigators have testified that witnesses allegedly described Ortega as the leader of the group and said he beat the victim and repeatedly kicked her and punched her in the head.
In the days that followed, police also arrested Smith, San Pablo resident Ari Morales, 17; Pinole resident Marcelles Peter, 18; and, Richmond residents Jose Montano, 19, and Elvis Torrentes, 22.
The seventh defendant, Richmond resident John Crane Jr., 43, was arrested two months after the alleged attack on a cold-hit DNA match, police said. His semen was found on numerous parts of the victim's body, Stockwell said.
Smith, Morales and Peter were juveniles at the time of the assault but have been charged as adults.
A used condom found at the scene had Crane's semen on it along with trace amounts of semen possibly linked to Peter, Stockwell said.
Evidence collected from Ortega's body came back positive for the victim's DNA, Ortega's sperm, and sperm from an unidentified male, Stockwell said.
Ortega's shirt had his own semen on it, as well as Crane's semen and the victim's blood, Stockwell said.
DNA from an unidentified male was also found on the victim's neck, Stockwell said.
A degraded sample of Montano's DNA was found on an open condom wrapper collected at the scene as well as on a can of Four Loko, an alcoholic beverage found at the scene, Stockwell said.
Peter's DNA was also found on the can, Stockwell said.
Ortega's DNA was also found on another alcoholic beverage container.
DNA from the remaining three defendants, Smith, Morales and Torrentes, was not found on any pieces of evidence collected at the scene.
Witness statements, however, have placed all of them there.
Richmond police Detective Stina Johanson, who finished her testimony this morning, said she found the victim's cell phone in Smith's dresser drawer, and Peter allegedly admitted that he fondled the victim, Johanson said.
Morales allegedly admitted to a different investigator, Richmond police Detective Ken Greco, that he inserted the antenna of a walkie-talkie into the victim, urinated on her and stole her ring, Greco said.
Statements from several of the defendants have placed Torrentes at the scene, according to detectives.
Stockwell's testimony will continue Thursday in Contra Costa County Superior Court in Martinez.