Toni Hartzong

Burns calls to the stand a neighbor of the Hartsongs named Carol Parkman.

She testifies she heard Bob and Tony arguing around 1 o'clock, the time investigators believe the murder occurred.

Investigators say lunchtime was Bob's window of opportunity.

His cell phone records show no calls between 1230 and 141, even though he was on the phone constantly the rest of the day.

That's when Burns believes Bob was at home arguing with Tony.

As for the knife used to stab Tony, Burns believes it came from this open kitchen drawer in the crime scene photos.

Under questioning, Bob told detectives that was the drawer where he and Tony kept their favorite knife, which they used to cut tofu.

Slightly serrated, but it was a very smooth knife.

It was like a paring knife?

Yeah, it was longer than a paring knife.

It was about...

about five or six inches, something like that.

And Bob tells investigators that knife is missing.

The last time you saw it, was it in the sink or in the drawer?

The only time I would ever think other than when I used it, it would be in a drawer.

So you think the murderer was committed with that tofu knife?

But Burns' most compelling piece of evidence is that trace of Bob's blood found under Tony's left thumbnail.

Tense moments in court as the jury listens to the tape of his interrogation by Springer and Van Houten.

I have no idea.

Today, Bob admits the blood might be his, but he has an explanation.