You pretend this is some obvious fact, but obtaining a search warrant against a person or property that were uninvolved in the crime but may have only been 'witness' to it is not obvious or clear to me.
The standard for getting a search warrant is probable cause, and that includes just probable cause to believe that there is evidence of a crime at the place to be searched.
Taking the witness analogy, even an actual person who's a mere witness can be compelled to testify with a subpoena.
A lot of places, talking to police is a very bad idea both because of the police and the other people in the neighborhood. You could very easily get shot for doing so.
Taking the witness analogy, even an actual person who's a mere witness can be compelled to testify with a subpoena.