"I honestly don't know why I'm here," 16-year-old Joshua L. Smith told a sex crimes investigator at St. Paul police headquarters on Sept. 28, 2006.

When Sgt. Jennifer O'Donnell told him a 17-year-old girl had claimed "you forced her to have sex." Smith denied it.

He also denied that the girl had ever been at his home on Stinson Street on St. Paul's East Side, according to a tape-recorded interview jurors heard Friday.

Smith, now 18, is on trial in Ramsey County District Court on two counts of first-degree criminal sexual conduct. He is accused of raping the 17-year-old, who has mental and physical disabilities, on Sept. 8, 2006, in the basement of his home. He also is charged with raping and beating a 57-year-old woman in the parking lot behind the Salvation Army building on Payne Avenue shortly after midnight New Year's Day 2007. Both attacks happened when Smith was 16; he was certified to stand trial as an adult.

O'Donnell told Smith during the interview that he'd been arrested on suspicion of criminal sexual conduct and read him his rights, but he agreed to talk to her.

"Are you sure you never had sex with her?" O'Donnell asked.

"Sure," Smith said.

"Are you sure she never gave you [oral sex]?"

"Sure."

O'Donnell told Smith that she had the victim's underwear and it had DNA on it.

"Here's your opportunity to be honest with me," the investigator said. " ... I need to know what happened."

"I told you what happened," Smith said.

Smith was not charged with raping the 17-year-old until after the New Year's Day rape.

Jurors also heard Friday from Mary Kasten, a trauma nurse who treated the 57-year-old victim at Regions Hospital in St. Paul. Kasten, who also is trained as a sexual assault nurse examiner, said she took a swab from the victim's mouth so it could be checked for DNA evidence. The swab was sealed in an evidence kit and turned over to the St. Paul police, who in turn gave it to the state Bureau of Criminal Apprehension (BCA) for testing.

Normally an oral swab would be done during the sex assault exam, but the victim had more immediate medical needs. Kasten said the victim was thirsty and Kasten knew that giving her water could wash away an possible evidence in her mouth.

Steven Swenson, a forensic scientist for the BCA, was the last to take the witness stand Friday.

He testified that semen was found on the 17-year-old victim's underwear, on the oral swab taken from the 57-year-old victim by Kasten and on a genital swab taken from the 57-year-old victim during a sex assault exam.

There was no testimony Friday about whose semen it was. The trial is expected to resume Monday.

District Judge Margaret (Peg) Marrinan told jurors that they could get the case Wednesday or Thursday.

Pat Pheifer • 651-298-1551