In what one critic describes as a signpost of our "always-on, surveillance society," police departments increasingly have been secretly using GPS, without seeking search warrants, to track the movements of uncharged suspects.
The satellite technology can be highly effective for this purpose: Although authorities are reluctant to discuss their investigative techniques, GPS has apparently resulted, for example, in the arrest of a convicted rapist in Virginia after a series of attacks on women in Fairfax County and Alexandria, the Washington Post reported. "After his arrest on Feb. 6, the string of assaults suddenly stopped." None involved a rape, notes an NBC article.
A Fairfax police detective had placed the device on the suspect's van, in a few seconds, while it was parked on the public street, the newspaper writes. It apparently helped them catch the suspect Feb. 6 as he was allegedly dragging a woman into a wooded area in Falls Church. He was not charged in any of the prior attacks.
Evidence marshaling software MarshalPlan
It's here: the law of evidence on Spindle Law. See also this post and this post.