josh mankiewicz: publicly, marcia clark seemed highly confident in her case back then. ase has been filed means that we do have sufficient evidence to convict him. josh mankiewicz: but privately, as clark told us, she sensed trouble early on. right off the bat, we've got a big push back in the african-american community. they don't like this case. they don't want to believe it. there was a sense of loyalty of investment in protecting an african-american icon who had made it. he was successful. he had made it. they did not want to see him taken down. even though he'd done virtually nothing for the community he'd come from? it was surprising. virtually nothing. this was not exactly your civil rights firebrand. and as he was quoted famously saying, i'm not black. i'm oj. josh mankiewicz: still, clark says she was convinced a strong case could be built primarily on the blood and dna evidence. marcia clark: there was a trail of evidence literally from bundy that led all the way into his bedroom at rockingham. and that included the blood, the hairs, the fibers. it was a huge a

marcia clark: can you demonstrate for us how loud it was? somewhat yes. marcia clark: go ahead. yeah, go ahead. and where did that noise seem to be coming from? from the back of the wall. josh mankiewicz (voiceover): kato kaelin had come to hollywood looking for fame. what he found was something more powerful, longer lasting, and ultimately upsetting. suddenly, you are a key witness in a very high-profile murder trial. what's that like? well, considering that i have never been in court before, i never had a parking ticket or speeding ticket, the first time in a courtroom is for a double homicide, it was-- it was probably the scariest moment in my entire life. and also, everything that you ever done in your life became out to the public. this is not what you wanted, i'm sure. i would never think, in a billion years, that this was going to be my life, how i was going to be involved, at one time, being a kid watching football, knowing who oj simpson was, how my life would just roll like, i'm living with oj simpson's house. this is-- oj simpson is up for trial of murder, and kato ka

nbc's kelly o'donnell has a report. - [kelly] marcia clark is playing it straight. ter] simpson smiling. johnny cochran laughing, as prosecutors struggle to explain why the killer's bloody gloves did not appear to fit oj simpson. - he had money and influence and could wheel those things to get the best lawyers available to him. - if it doesn't fit, you must acquit. if it doesn't fit, you must acquit. - and watching that, i was like, oh, this is not like if me or somebody i knew was accused of a crime. this is like celebrity. this is theater. - i've always wondered, is there really a difference between the trial of a century and a circus? because they seem to go hand in hand. - it became a joke on the tonight show with jay leno and the dancing itos. - the dancing itos with special guest, marcia clark! ladies and gentlemen! - i'm so saturated by the irresponsibility of the media that i'm beyond being outraged. i mean, i'm almost numb to it at this point. - this isn't a punchline. this is murder. - [kelly] today, the final act in what has been a national obsession. what