Written on the Sleeping dogs forum by one of the mods -
"Hi everyone, so I've looked into this and just to skip to the end, the SWAT cruiser, outfit and assault rifle are only available to use during the mission - you can't use them in the open world.
Now, I appreciate that this is probably not what you wanted to hear and may even come as a bit of surprise, but to be 100% honest, I'm not sure where the confusion is coming from.
Take a look at this image: http://www.gamersbliss.com/wp-conten...s-gamestop.jpg
It states up in the top right that it's the mission that includes the SWAT attire, police car and weapon, rather than being extras for your wardrobe and garage.
That said, I've flagged this to our Production team who are going to investigate this and see if we can alter this functionality in a future title update so that when you finish the mission, you still have access to the car in your garage and the outfit in your wardrobe.
Just to manage your expectations, there's no timings for this right now - rest assured, though, if this were to happen I'll let you all know as soon as I receive an update."