Head through the parking garage and open the door to the elevator controls room using the diamond key.
Resident evil 2 locked door parking garage.
Grab the equipment disposal notice and the box off the table on your right.
From the parking garage head straight down the hall and go through the first door on your left to find the firing range.
Next to the magazine is the police station map b1 along the wall but the elevator controls room is locked by a diamond door.
Be sure to check the elevator itself for a small note then head back.
For resident evil 2 on the playstation 4 a gamefaqs message board topic titled is there any way to access the locked door in the parking garage.