When did the CSI 과학수사대 Las Vegas team shift from forensics only to carrying weapons, interrogating witnesses, etc.? Was the procedural change duscussed on show 또는 just a shift in a particular season and not explained?

It wasn't directly addressed on the show, but I'd assume the change took place around the time CSI: Miami aired and gained popularity. Miami was known for the big action sequences and gun fights. I think this CSI 과학수사대 wanted to go the direction they were going, and it also gives the characters much 더 많이 to do.