To complete the medallion puzzle you’re going to need to blow up some C4 and get one of your first tastes of the Resident Evil 2 puzzle solving mechanics. You’re going to need to find two items to make this happen and then combine them to blow up the explosive device.
Get the Electronic Gadget & Battery
You’re going to need both the electronic gadget and the 9 Volt Battery to blow up the C4. You can find the Electronic Gadget in the first floor of the west side of the Police Station just south of the Operations Room. You will need to the bolt cutters to access this area so you should have at least progressed to the fire escape where you meet back up with Claire for the first time.
You can find the Battery in the S.T.A.R.S. Office in the small room that is immediately to the left when you walk in the room. Once you have the 9 Volt Battery and the Electronic Device you can combine them from the inventory screen and take them to the West Storage Room on the third floor (3F). You’ll need to place the combined items which will now be called the Detonator on top of the C4 and arm the charge. After a brief countdown the explosives will detonate and then you will have access to the Maiden Statue which will give you a puzzle to solve and a medallion.