This is during PW: AA, Ep. 4
Investigation (Day 2): Part 2
You need to meet up with Detective Gumshoe at Criminal Affairs Dept. as he'll unveil his three secret weapons!
Here's how I earned the trophy:
Borrow the fishing rod. move to Gourd Lake Woods where you'll get a bonus interaction.
Return to Gumshoe and ask to borrow his secret weapon.
You'll return the rod and this time borrow Missile (K-9 Police Dog). Go to Gourd Lake Public Beach where you'll get a bonus interaction.
Return to Gumshoe and ask to borrow his secret weapon and this time borrow the metal detector. Once given, that should earn you the trophy automatically.