To lock up the mall and keep zombies from getting in, you need to park the trucks over the entrances. Get the key from the office on the 2nd floor and go to the 4th floor where the keys to the trucks are kept.
To keep the dead zombies from coming to un-life, lock them up in the freezer in the basement.
Before you can go play in the basement, you need a source of light. Get the fuses and gloves from the 3rd floor and go to it!
First get Alex to drop the helicopter keys by the helicopter, there's no point in carrying them around with you and it will enable you to carry one more useful object.
Choose one of the characters and go down to the security room on the second floor, pick up the set of keys and make your way to the list, don't bother getting any weapons and don't stop to kill any zombies.
Use the keys and now you will be able to go up to the fourth floor (drop the keys in the lift, you don't need them any more). Leave the lift and you will now be in the main control room, and here you will find three different keys on the floor, each one of the three will start one of the lorries, enabling you to move them.
Via the lift now make your way back down to first floor and go to each of the lorries and using the keys move them in front of the various entrances to the shopping centre. The only problem is now that your character will not be able to get back inside. Choose another one of characters and send them down to the sports shop on the third floor, get the rope, and then go to the balcony above the front entrance on level two, use the rope and you other character will climb up and onto the balcony away from danger. Get one of your characters to get the fuse, the rubber glove and a gun, an make another character to get the torch, take them in the lift to the basement and get the person with the torch to use it so when you exit the lift you'll be able to see where you are.
Both go round to the fuse-box and after you've disposed of any zombies get the character with the rubber glove to use it and insert the fuse into the fuse box. Now using yet another character go to the forth floor and press the buttons on the computer to activate the lights in the basement. This is where operation zombi kill starts. Get one of the characters to go round each of the levels destroying all zombies he meets and then stick all the zombies in the cold store (if you use the tape from the video shop with the TV and video in the rental shop you'll see that you have to shoot the zombies in the head to kill them). If you now go down to the main entrance you will see that some thugs have moved the lorry and have made their way inside.
Getting the fuel can (level three), a gun (level two), and the hose pipe (level one) go outside and go to the right. Soon you will come across a van belonging to the thugs, shoot any thugs that are by the van, and then drop the fuel can in front of it. Now use the hose pipe and, viola! You now have the precious fuel you need to fly away in the helicopter. Get everybody inside the helicopter and start it up with key (remember where you left it) and the game is completed.