This is not "some point in an investigation / trial", this is a specific point. They have a warrant. I'm not a big fan of "compelled evidence" (gathering DNA,

This is not "some point in an investigation / trial", this is a specific point. They have a warrant. I'm not a big fan of "compelled evidence" (gathering DNA, blood or fingerprints from a suspect), but the courts have been saying it's ok, and that's the approach they're taking here. They just can't (so far, in the US) compel you to actually produce testimonial evidence like passwords, passcodes, etc.