There's nothing wrong with accepting packages not addressed to you, especially from FedEx, what you're thinking of is 'opening someone's USPS mail' which most definitely is illegal.
If it was illegal to sign for a package addressed to someone else how come FedEx will let just about anyone sign for a package, even when you say they aren't home.
So in essence, you're saying it's ok for police to use evidence of doing nothing wrong as evidence of a crime?
There's a big difference between signing for someone who's not home and signing for someone that you know for a fact not to live there. It's not a criminal offense, but the standard for probable cause is one of suspicion rather than proof of criminality.
Well, to be precise, "reasonable suspicion" is a weaker standard than the "probable cause" required for a warrant. In either case, there needs to be suspicion of something specific, not just "this seems shady".
That said, you are certainly correct that "probable cause" is less than proof, and knowing nothing about the case it seems plausible that "this guy is accepting packages for people he doesn't know" firmed up some link in their reasoning and made the difference between lacking and having probable cause.
If it was illegal to sign for a package addressed to someone else how come FedEx will let just about anyone sign for a package, even when you say they aren't home.
So in essence, you're saying it's ok for police to use evidence of doing nothing wrong as evidence of a crime?