First thing you'll want to do is take your red mazda car you bought with your fancy-smancy bucks as a prosecutor and drive to the local Home Depot

Next locate and secure a route to the entrance and proceed with the most normal and cool running animation

Once inside, locate the key crafter and get the required materials

you'll need 6.99 USD

this can be gotten by not buying incriminating confectioneries from the court vending machines while also avoiding a DL-6 level incident whenever you get put on trail

This is by far the HARDEST part of the entire process as you are left to wonder:

what little nick-nacks you can get for your key, whether or not your key should be a knife, deciding between; the dog, hello kitty, or spiderman decals, whether the knife should also be a key, and what key-chain screams NARUMITSU the most

YOU DID IT!!!!
(cue confetti and a slash in Gumshoe's pay for wasting tax money on confetti)

Now you can update the autopsy report AND the key to your car! congrats!