LOS ANGELES (AP) _ After three days of testimony from Brian ``Kato'' Kaelin, the O.J. Simpson prosecutor had heard enough.

An angry and frustrated Marcia Clark implied Thursday that Kaelin wasn't just a guy whose thoughts were as disheveled as his blond hair. Instead, she suggested the quirky house guest was helping to cover up for a murderer by hiding details of angry battles between Simpson and his ex-wife.

In an unusual attack on her own witness's credibility, Clark treated Kaelin like a man with something to hide. She grilled him at every opportunity about Simpson's demeanor and physical appearance before and after the killings of Nicole Brown Simpson and Ronald Goldman.

Discrediting Kaelin is risky for the prosecution, because his testimony about a burger run to McDonald's and subsequent bumps in the night created what prosecutors call the ``window of opportunity'' for Simpson to commit murder.

``The prosecution played a tough game of trying to attack Kaelin's credibility on some issues while keeping the view that his timeline was truthful,'' said Loyola University law professor Stan Goldman. ``As my mother would say, it's hard to ride two horses with one body.''

The defense, which treated Kaelin gently on cross-examination, seemed to welcome Clark's high-wire act.

``By calling a witness, you are implicitly vouching for that witness's believability,'' Simpson lawyer Carl Douglas said out of court. ``For her now to go back and now attack her own witness is a very risky tactical choice to try.''

No testimony was scheduled for today. Kaelin was to return for more questioning Monday.

It was difficult for both sides to get clear answers out of Kaelin, an aspiring actor with an amusingly goofy personality who was living in Simpson's guest house at the time of the killings. He often shifted in his seat, gulped water or applied lip balm while on the stand.

When asked if people at Simpson's house were in shock the day after the murders, he answered: ``Yes, the TV was on.'' But despite his often disjointed testimony, Kaelin insisted he has always told the truth.

``There's nothing I tried to hide from you,'' the rattled witness said beseechingly to Clark at one point, trying to explain why he never told a grand jury last June that one of the fights led to a 911 call.

``I knew if it was a 911 call there would be a report,'' Kaelin rambled. ``I was in front of all these people...''

``So are you telling us now that you felt intimidated by the grand jury, Mr. Kaelin?'' Clark snapped.

``I don't know if intimidated is the word, but I tried to remember everything that I could,'' Kaelin replied.

``Do you remember telling me, Mr. Kaelin, that you had thought that being in front of a grand jury would be intimidating, but it turned out to be just a bunch of old guys in fishing caps?'' Clark asked, drawing snickers in the courtroom.

``Yes,'' he replied.

The court day ended with Clark springing a question on Kaelin about a former Simpson maid, Michelle Abudrahm.

``Do you also recall that Michelle was the one who opened the door to let the defendant into the room to beat Nicole in 1989?'' Clark asked. There has been no evidence at the trial to support that question.

Simpson flashed a look of shock, and defense attorney Robert Shapiro quickly stood and objected.

A lengthy sidebar discussion followed, and the jury was instructed by Superior Court Judge Lance Ito to ``completely disregard'' Clark's last question since Kaelin ``was not acquainted with anyone in this case in 1989.''

Clark implied through much of her direct and redirect questioning of Kaelin that he had cooperated with Simpson and his attorneys, speaking with them several times in the days after the murders and visiting with Simpson.

Under an almost friendly cross-examination by Shapiro, Kaelin acknowledged witnessing two heated battles between the Simpsons, but insisted Simpson ``never let on that he was upset about her dates.''

But when questioned by Clark, Kaelin said that when Simpson and his ex-wife battled one night in October 1993, it was about Ms. Simpson keeping pictures of an ex-boyfriend.

``And how angry was he that day, Mr. Kaelin?'' Clark said.

``Angry. He was yelling. The police came.''

``Would you say he was very angry?''

``Angry enough for the police to come. Yes.''

Kaelin also described a fight on Christmas Eve 1993.

At one point, Clark asked, ``Did you say to the grand jury that O.J. called Nicole a bitch?''

``No,'' Kaelin said, as Simpson appeared distressed by the question.

Clark got Kaelin to admit that he told the grand jury nothing about the Christmas Eve fight. Kaelin also acknowledged that he didn't give the grand jury some of the more dramatic details of the October fight, including the fact that Simpson smashed through his ex-wife's back door.