Evidence from another country?
I'm asking mostly from the U.S. perspective, but would evidence of crimes in country A, that is acquired in country B, be admissible in country A? To be more concrete, someone commits a murder in the U.S. and flies to the UK. The UK police do a search of their phone (not necessarily at the border) and find evidence that they committed the crime in the U.S. Could the UK police just send that evidence to the U.S. and it be admissible? What about another country? Especially if that country were a little looser on what constitutes "civil rights." I don't think I'm specifically asking about extradition, that usually requires initiation by the extraditing country.