OSHKOSH, WIS., NOV. 8 -- A 29-year-old Oshkosh man was found guilty today of felony sexual assault on a woman who claimed that he took advantage of her multiple personality disorder to coax one of her personalities -- a naive and compliant one -- into sex.

Defendant Mark Peterson, an unemployed man whose last job was as a grocery store bagger, sat without expression as the jury of six men and six women returned the verdict after a four-day trial. His mother, in the audience, wept quietly into a tissue.

The case had attracted widespread attention because the 27-year-old victim presented herself as a single body encompassing scores of separate personalities. For the jury and a fascinated crowd of court spectators, the woman had repeatedly lowered her head and then raised it again to speak in what she explained was the voice of a personality whose name, age and sometimes even gender were different from the one who had just finished speaking.

Peterson faces a maximum 10-year sentence for violating a Wisconsin law against knowingly having sex with a person too mentally disabled to assess his or her conduct. Sentencing has been set for Dec. 10. After the announcement of the verdict, a crowd of reporters chased the stony-faced defendant down the courthouse steps.

"I've been the victim here," Peterson said as the reporters backed him into a downstairs corridor. "I'm charged with second degree sexual assault for just having a fling with a girl."

As he had on the stand during his two hours of testimony this morning, Peterson denied that he had been told of the woman's disorder before having sex with her last June in the front seat of his car. "I'm going to appeal. I'm looking for a different attorney," he said. "I did not know she was mentally ill -- I still don't think she's mentally ill."

The jury foreman, University of Wisconsin finance professor David Ward, said the jurors argued about that during their six hours of deliberation -- about what Peterson knew before having sex with the woman who has been referred to in these articles as "S." The woman said today that she did not mind reporters' use of "Sarah," which is her legal first name but which applies to only one of the 46 personalities that she testified exist within her mind.

"The question of multiple personality disorder was one of the things we did debate," Ward said. "There are some, I think, on the jury, just as there are some experts, who believed it more than others. But the bottom line was that she did suffer from a mental illness, and the defendant was aware of that."

The jurors originally voted 8 to 4 for conviction, Ward said, but what swayed the four holdouts was a statement Peterson gave to Oshkosh police after Sarah brought charges against him. Sarah's complaint contended that neither she nor most of her other personalities knew about the sex act in Peterson's car -- that she learned afterward that Peterson had deliberately summoned a naive 20-year-old personality named "Jennifer" because he thought she might accommodate him sexually.

In his police statement, Peterson had made repeated references to "Jennifer," adding at one point, "A 6-year-old was popping out when I was making love to Jennifer." Although Peterson testified on the stand today that his police statement was inaccurate and "screwed up," Ward and two other jurors said the statement convinced them that he knew before their sexual encounter that Sarah was mentally ill.

"This is not a case of somebody going into a bar, meeting somebody, going home and having sex, and then later finding out she had a mental illness," District Attorney Joseph Paulus said after the verdict. "This is a case of a man who knew about it before, found out about it, and preyed on it to get what he wanted."

The case was apparently the first example of a crime victim bringing charges based in part on her multiple personality disorder, and Paulus said he hoped it might expand legal protections for the mentally ill. "When people intentionally manipulate someone who has a mental illness," he said, "they will be held accountable in the eyes of the law."

Multiple personality disorder itself was not technically at issue in the trial, since the jury had only to find that Peterson knew the young woman was too mentally ill to "appraise" her own conduct. But Paulus tried to convince the jury of the seriousness of multiple personality disorder by calling to the stand psychiatrists and finally Sarah herself.

The verdict, brought in at 7 this evening, followed two hours of testimony this morning in which Peterson insisted he never saw any evidence of unusual behavior in Sarah until he brought her home after their sexual encounter in the park. Two days earlier she had originally introduced herself to him as Franny, he said, and when she later mentioned such names as Jennifer, Sarah and John, he did not understand that she was talking about people who lived within her own mind.

"I thought she was talking about her sisters and her brothers," he said.

The prosecution contended that Peterson was told about the multiple personalities beforehand both by the woman and by her downstairs neighbors. But Peterson, wearing a dark blue suit and looking directly at his lawyer as he answered each question, said no one told him Sarah was mentally ill.

"Did anybody say to you that Sarah is deficient or mentally ill?" Peterson's attorney, Edward Salzsieder, asked his client as they talked about the evening last June when Peterson first struck up a conversation at a park with the young woman who had told him her name was Franny.

"No," Peterson said.

"Did the name or personality of Emily ever come up at that time?" asked Salzsieder, referring to what Sarah and her psychiatrists have described as a personality with the vocabulary and maturity of a 6-year-old girl.

"No," Peterson said.


"No," Peterson said.

"Are you positive?" Salzsieder asked.

"There was no names said about anybody coming out at that time," Peterson said, his voice contained, his head cocked slightly in the direction of his lawyer. It was true that he and the young woman had gone out for morning coffee two days after meeting in the park last June, he said, and that they had driven to a park afterward and had sex in his car. But he thought he was spending the morning, he said, with the woman named Franny who had talked to him over coffee about people with names like Jennifer and Emily and John.

"I thought I was having sex with Franny," Peterson said.

He said it was not until he and Sarah returned to her house from the park that he watched what appeared to be her switching of personality -- the rapid behavior changes that resulted in her alternately acting like a 6-year-old girl, a 20-year-old woman, a 32-year-old woman and an animal-like presence that growled and crouched under furniture.

"Were you surprised at times -- this display of many in one body?" Salzsieder asked.

"I was very surprised, yes," Peterson replied.

Was it true, Salzsieder asked, that the woman told Peterson that the 6-year-old Emily had been "peeking" from somewhere within Sarah's body during the sex act -- and that Peterson tried to contact Emily to make sure she said nothing about it afterward?

"I asked for Jennifer to ask Emily to forget what she saw," Peterson said. "Because it was between me and Jennifer."

"Not sex between you and a 6-year-old," Salzsieder said.

"Right," Peterson said.

Wednesday evening a psychiatrist for the defense testified that he did not believe Sarah suffered from multiple personality syndrome at all -- that he believes this is a newly fashionable diagnosis many psychiatrists do not accept.

"There's a band of very intense believers who have all the sightings, where the rest of us never see any," said Darold Treffert, a Wisconsin psychiatrist who reviewed Sarah's psychiatric records for the previous year. "What I call the UFOs of psychiatry."

Treffert said he did believe Sarah had psychiatric problems, but that her illness did not appear grave enough to fit the requirement of the Wisconsin statute under which Peterson was charged.

"It was a hard decision, a very hard decision," said juror Cindy Lancaster, a mechanical designer who in early deliberation was prepared to find Peterson not guilty. Although she herself was not persuaded that Sarah exhibited real multiple personalities, she said she had no doubt that the young woman was mentally ill.

"I just think it's another sick woman who needs help," Lancaster said. "I believe that the rights of the mentally ill need to be protected against sexual assault. And I hope we did the right thing."