September 12, 1995 -- 8 p.m. EDT
From Special Assignment Correspondent Art Harris
LOS ANGELES (CNN) -- O.J. Simpson's defense team is investigating possible evidence they hope will impeach someone they call a "key" prosecution witness, a defense source told CNN Tuesday.
Within a couple of days, the defense expects to know if the evidence will be solid enough to present in court. And while the identity of the so-called "mystery witness" is unknown, a defense source told CNN the defense is looking into evidence they hope to use to challenge the credibility of Los Angeles Police Detective Philip Vannatter, a 27-year veteran of the department and a key prosecution witness.
After discrediting retired Detective Mark Fuhrman, the defense has been trying to dig up dirt on other officers who helped build the double-murder case against Simpson.
The defense source told CNN the team has received anonymous tips about Vannatter, and is investigating them. "We don't know if it's real, but we're checking (them) out," the source said.
Informed of the purported investigation, Vannatter told CNN, "Everything I testified to is exactly as it occurred, and as I remember it. Whatever they come up with is bull----."
Another defense source, however, told CNN the mystery witness Cochran has been talking about is not someone who will undermine Vannatter, but someone else involved in the trail. The source predicted the move will be "very controversial."
"It has to do with something totally different and will be devastating," the source said. "If it's the witness I'm thinking about, put in the proper context, it could have national consequences."
Meanwhile, another defense source tells CNN Simpson's attorneys are continuing to explore any leads about witnesses who could contradict Vannatter's testimony that he first met Fuhrman at the Bundy crime scene.
"The first I ever laid eyes on Mark Fuhrman was the morning of June 13, 1994," Vannatter said Tuesday.
Vannatter works in the elite robbery homicide division. In June 1994, Fuhrman worked across town in the West Los Angeles Division.
On his way into court Tuesday, Simpson attorney Johnnie Cochran said, "I never said this had anything to do with Vannatter."
The mood of the prosecution has soared since last week when a deputy district attorney told CNN, "We've lost this case. The best we can hope for is a hung jury."
But this week, the mood of the prosecution seems to have lifted as Marcia Clark hammers away with evidence on the glove recovered from the crime scene, DNA and other matters. "We've got overwhelming evidence and we're a long way from giving up," one prosecution source told CNN. "But sometimes we do feel like the underdog."
In a bizarre twist to the question of Simpson taking the stand, the defense team has brainstormed at least one novel way to try it. Sources close to the defense told CNN lawyers discussed putting Simpson on the stand, with Johnnie Cochran quizzing him. On direct examination, he would assert his innocence, then take the Fifth Amendment, outside the jury's presence. That would deny the prosecution the ability to cross-examine him, the idea went.
There's a problem with that strategy, however, a prosecution source told CNN. Once Simpson agrees to testify, he has waived his Fifth Amendment rights and can't refuse to answer questions during cross-examination by the prosecution. "There's no case law to allow what they're talking about," the source said.
After exploring the novel strategy, the defense has apparently dropped it as an alternative.
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