Make your way out to the Cambridge Police Station. If it is your first visit you will encounter Paladin Danse fighting off a horde of Feral Ghouls. Help him clear them out then follow him inside. Once inside, head through the first door on the left.
Turn to the right after that and head toward the hallway in front of you.
Go left inside it then enter the second door on the right. Just inside, look for the Cambridge Police Evidence Terminal (Novice Hack)