Prosecutors Say David Pietz Failed Polygraph

Pietz is on trial seven years after allegedly killing his wife.
3:00 | 10/08/13

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Transcript for Prosecutors Say David Pietz Failed Polygraph
The latest on the seattle husband on trial for murdering his wife, seven years after she was killed. She flunked a polygraph test right after her death. And emotions, as you can imagine, are running high in court. Abc's neal karlinsky has the latest on this dramatic case. The cause of death was asphyxia, due to strangulation. Reporter: For a dozen of friends and family of nicole pietz in court, monday was difficult. She wasn't just strangled by a stranger on the street. But by someone lying on top of her, as they believe her husband, david, was. That scenario could be consistent with the pattern of bruising we're seeing. Reporter: David pietz had been telling co-workers he thought something happened to nicole, while she was on the prowl for drugs. She was supposed to be going to an aa meeting. And she didn't return home. So, he believes that it was basically a drug deal gone bad. Reporter: According to testimony, toxicology reports show she had small amounts of prescription drugs in her body. And no signs of recent abuse. Prosecutors also raising the issue monday of a lie detector test david pietz failed at the time of the murder. Pointing out he evoked his rights and refused to take another one six years later, when he was finally arrested for murder. We all know that, in fact, he did -- you know it. Their assumption is going to be that he didn't talk because he's guilty. Reporter: The fact that he said no to a second lie detector test won't be heard by the jury. Defense attorneys argue, to block testimonies from a co-worker of pietz. He called detectives every year to check in on the hunt for his wife's killer. Police say, they did not hear from him yearly. Yes, the events happened seven years ago. He happens to be on trial today. And what your client says is still of note. Reporter: David pietz claims he is innocent. His attorneys will begin arguing their side of the case later this week. For "good morning america," neal karlinsky, abc news, seattle. We're going to bring in abc chief legal affairs anchor, dan abrams now. So much out of the jury, talking about the lie detector tests. And he refused to take a second. But the jury will never hear this anyway. The prosecutors know they will not be able to introduce the results of a polygraph. What they were saying is, surrounding this offer of taking a second polygraph, there was a lot of back and forth, in effect, between the police and the defendant. They want to introduce some of the conversations. In the end, the judge is basically saying, polygraph is taboo. Polygraph tests have been inadmissible. We're not going to allow even questions that suggest he could have taken a polygraph or might have taken a polygraph. We all know this. Why did authorities have the tests taken? It's a good question. It helps the police in an investigation, right? It's a tool for them to determine do they believe They can also use it as a threat, et cetera. But it's not admissible. So, they can use it as an investigative tool. But they know when it comes to the actual trial, they're not going to be able to introduce the results. Something the jury has been able to hear, the witness who was said, that the husband claims that the wife may have been involved in some shadiness. I think this is one of the most important things that's come up in this case. This is this idea that the husband had said to someone, i think this might have been a drug deal gone bad because she had some substance abuse problems, et cetera. The reason I think that's so important is because the jurors are going to dislike him for that. This is a woman who is dead. And her husband is saying, this might be a drug deal gone bad. A lot of people are going to look at that and say, why would he say that? Why would he think that about her? And that could be a problem. It's been a very bizarre case. A much lighter controversy right now.

This transcript has been automatically generated and may not be 100% accurate.

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