Dead Island 2 has the player traveling around many of Los Angeles', or Hell-A as the game calls it, locations and points of interest. One such location is Venice Beach, of which where you save a group of survivors currently holing up in the Blue Crab Restaurant. One survivor, Trent, has an interesting proposition for you; to raid the local Police Department for weapons to arm his fellow group of survivors.
Once you agree to his plan, he'll warn you of the very likely demise of the police department's workforce; be prepared for the Z's in uniform along the way.
Beginning The Mission
The Los Angeles Police Department is southeast of the Blue Crab Restaurant; directly down the main street that leads you out onto the beachhead. It's hard to miss the Police Department as its building's outline is the only thing jutting out of the horizon against the ocean other than palm trees. Mind the local shops and avoid the potential Crushers to the left.
Weave through some Zombies and walk over a small grassy hill, and you should now see the Police Department proper, with Police Walkers and Shamblers standing around the parking lot. They're no different from regular Walkers or Shamblers, so slice away as you normally do. Just make sure to not hit any of the Patrol Cars, or you'll set off a car alarm. The entrance to the building is on its far left side, it's unlocked so just walk in. Not feeling confident about taking this on alone? Try playing with friends!
Accessing The Front Office
The first obstacle you'll face when entering the LAPD building is its Maglock door that's preventing you from going further inside. How Maglock doors work is through electric panels connected to the door through wiring around the area; they're usually hidden from an obvious first glance.
1st Maglock
The 1st Maglock panel is through the security window to your left when you first enter the reception area. Use a ranged weapon to shoot at the panel to destroy it, releasing the first lock on the Maglock door. If you don't have a ranged weapon so far, you can try throwing your melee weapon at it; just make sure it's small enough to fit through the security window.
2nd Maglock
The 2nd Maglock panel is a little easier for a player to stumble upon as it's located just ahead inside the bathroom as you enter the reception area. This panel is close enough for the player to hit it with a melee weapon, so feel free to save a bullet and smack it with your favorite sword. With both of the panels now destroyed, the Maglock door will open; giving you access to the Front Office.
Getting Inside The Back Office
Now that you've gotten into the Front Office, you'll need to head deeper into the station to get to the Storage Room; but to do that you'll need to get into the Back Office. The Front Office comprises its Front Office Reception Area, Hallway, and one locked Cell; the other Cell is inaccessible. Down the Hallway is the door that leads into the Back Office, but it's currently locked by a Keycard Reader; it's asking for the Police Department Keycard.
Police Department Keycard Location
Finding the Police Department's Keycard is funnily enough exactly where you would look for in the first place; the key rack. Located in the back of the Front Office Reception Area, go ahead and grab it without much fuss; there are no Zombies inside there.
*Bonus: Jail Cell 02 Key
Before you go, try grabbing the Jail Cell 02 Key sitting atop the desk directly beneath the 1st Maglock panel. This key opens the locked Cell door within the hallway. Watch out for the Zombie that'll lunge at you if you open the door; once defeated, enjoy the crafting materials inside and the Disaster Relief Case. With the Keycard now in possession, go ahead and open up the door to enter the Back Office.
Getting Into The Storage Room
Now at the last stretch, the Storage Room is your final obstacle. The Storage Room is locked and requires the Secure Storage Room Key; inside awaits your prize and an extra surprise.
Secure Storage Room Key Location
Finding the Secure Storage Room Key simply requires the player to round the Storage Room to the right, of which the key is atop a service table connected to the cage. Go ahead and grab the Secure Storage Room Key and watch out for the stray Walker meandering inside the Back Office. With the Secure Storage Room Key now in your possession, you can open the Storage Room.
Gun Case Location
Hidden behind the Storage Room's middle pillar is your prize, the Gun Case for Trent and his group. Collect it by pressing X, this prompts you to head back to the Blue Crab restaurant and deliver the goods.
*Bonus: Rare Quality Assault Shotgun
What's a Police Department's Storage Room without a Weapon to loot? The Rare Quality Assault Shotgun is your reward for getting this far into the station, it's up for grabs along with Shotgun Ammo inside the open gun locker behind the middle pillar entering the Storage Room.
You complete the mission once you deliver the Gun Case to Trent; just don't expect him to remember you even going ahead and doing this in the first place. But he'll know what it's worth and give you $500 along with 3000XP for completing the quest.