Dear Viewers,

For those of you who have been following the Laci Peterson (search) murder case, you know that the police, in the days after her disappearance, tracked her husband Scott. They obviously were suspicious of him. The police used Global Positioning System (GPS) equipment and affixed it to cars that he drove (owned and rented) to see where he was went. While at this point we do not know exactly where he went (presumably we will get during trial,) the defense wants to exclude the GPS tracking information from the jury's consideration. While we assume the information is helpful to the prosecution (why else would the prosecution seek to use it), it is not inconceivable that even if it does not "hurt" Scott's defense, his lawyers would seek to exclude it.

On Wednesday night’s show we explored the "pros and cons" of the GPS tracking information.

Many viewers e-mailed me about it and here are some of those e-mails:

No. 1:
Greta,
As the wife of a vice officer who uses GPS on his job, I wish you would refrain from telling the public how it works and what to look for. In doing that, you have compromised the safety of undercover officers and possibly the jobs they are working on. Please use more discretion before asking for details such as location of devices, etc. Thank you,
Margaret

Incidentally, I responded to Margaret and told her that we exposed no secrets. GPS technology is common, e.g. it is now in cars and boats. We would not -- and did not -- compromise the safety of law enforcement officers and we would not knowingly jeopardize investigations. I try and be very careful in how we cover these stories. I want you to get the information without crossing the line and harming the prosecution, the defense, or law enforcement.

No. 2:
Still doesn't prove anything. I'd have to sit in the courtroom and hear all evidence, circumstantial as well as hard evidence before judging the individual. He went to that bay to fish, we know. So why would it be odd for him to go there any time? Plus, is "tracking" an uncharged person not an invasion of privacy, or legal? You’re a trained attorney… you be the judge of that. Have a good evening.

This viewer is in many ways right. GPS technology only proves where the cars went that had the device attached to them. It does not directly prove who murdered Laci. Note that if the evidence is admitted, the jury is permitted to draw a reasonable inference from the information and that is what may harm the defense. A reasonable inference could be -- and this is simply a guess on my part -- that the prosecution believes that travel to a particular place at a particular time is circumstantial evidence pointing towards guilt. Circumstantial evidence -- if reasonable -- is admissible.

No. 3:
Greta,
The GPS info should not be allowed in court if it is only 95% accurate. We are talking about a death penalty case -- a 5% error could be crucial.
Joan of Anchorage, Alaska

As long as a jury is aware of any possible error, it will likely be admitted. The jury will then decide whether that margin of error means the evidence should be discounted or not. There is no such thing as "perfect" evidence. Juries are often called upon to assign "weight" to evidence - meaning juries decide how important a piece of evidence is. Juries are free to disregard any evidence presented to them. Even medical opinions can be discounted by juries (and often two doctors will give two completely different opinions in the same trial and the jury must sort out who seems more knowing or more believable.) But, I do agree that in death penalty cases in particular that the judge, who is the gatekeeper on what evidence gets in or not, must be careful not to let the jury hear totally incredible or unreliable evidence.

And finally, here is one of my favorite e-mails of the night. If you watched the show, you will know that during the Peterson court hearing yesterday the judge was handed an envelope. The contents remain a mystery but it was a bit of a show for the audience. In order to "get" this e-mail, you must be a frequent TV watcher and know about an insurance ad that has been running:

Greta,
I think the letter the judge got said he just saved a lot of money on his car insurance by switching to _____ ! Hey next time your at Fort Leonard Wood stop by the fire station and I’ll have the coffee on .
Glenn

Glenn has a good sense of humor. I think I would enjoy that coffee at the fire station.

Greta

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Watch On the Record with Greta Van Susteren weeknights at 10 p.m. ET