1) After the boss fight, when Paul is on fire, DO NOT KILL him. Instead, pick up the fire extinguisher in the store to put out the fire.
2) Then bring Paul back to the security room. (You can also save the 2 women as well)
3) After a while, you will receive a call saying Paul has a present for you,
4) Go back to the security room to meet Paul, continue to talk to him and he will give you his Molotov Cocktail to use. (Unlimited supply!)