The device torn down was one given to them by a woman who kept it after being tracked in 2005: http://www.wired.com/threatlevel/2011/05/gps/

This story gives background on Karen Thomas, the environmental activist who was tracked by the device. http://www.wired.com/threatlevel/2011/05/gps/

The FBI demanded the device back and she said no. Amazingly, that was the end of the story—until the Afifi story came out, and she decided to give Wired the tracker.

The interesting legal question (in addition to whether you need a warrant to do this sort of thing) is who owns something attached to your car?

I'll be very interesting in hearing what the Supreme Court has to say about all this. Consider the following worst-case scenario:

1. Supreme Court rules that use of GPS tracking devices by law enforcement do not violate 4th Amendment.

2. Future court rulings find that tampering with GPS devices amounts to interfering with a police investigation.

3. Law enforcement starts planting GPS devices directly on persons, such as in a purse, or when miniaturized further, in wallets or attached to clothing. Maybe these devices only capture data "when in public areas" and are eventually declared legal.

4. Since they cannot be tampered with, police begin attaching wristbands to citizens stopped at routine traffic stops who they suspect of crimes.

Sounds far-fetched, but not when you consider the amount of surveillance that goes on already via cell phones and credit cards.

What do you mean "sounds far-fetched"?

There are people walking around with government installed GPS bracelets right now: http://en.wikipedia.org/wiki/Ankle_monitor

The interesting legal answer is... apparently iFixIt.

The article indicates that court rulings have been mixed as to whether a warrant is required. I suspect the FBI doesn't want to force the issue, in case they lose.

If the tracking were completely legally sanctioned, I can't imagine that the trackee would have any claim to ownership over the device.

To force the issue they'd have to prove they had the right to put it there in the first place, right?

Alternatively they expect these to go missing and it's not worth the hassle to get them back.

You do, as whoever put it there clearly intentionally abandoned possession of it.

I suppose if they really really wanted it you could send them the parts back.

I suppose its as simple as their demands not being met. "We want it back." "Nope, I already took it apart and posted it to teh intarwebs." "Well then."