What set does this Lego S.W.A.T van go to?
That gun is actually pure Lego. It's a Tommy Gun.

Your truck, however, seems like a custom MOC made of random clone-brand parts due to the randomness and low quality of the build. I doubt that a clone-brand company would publish that truck as a set if it looked like that.
I am currently failing to identify this part on your truck, it doesn't match the color scheme. It proves that your truck is made of multiple clone-brand parts from multiple sets, and maybe even multiple companies! I can not find anything like it in the google image search:

The closest I can find is this part, and here's the site it's hosted on:

From the comments:
You have also said that it says Lego on the studs, but I'm just going to assume that only some of them do because of that clone-brand part I've pointed out. Lego does not and will not make SWAT content, and besides that, the truck is a rather low-quality build, so it's certainly not &quot;from a set&quot;. Why randomly put a lattice tile on the roof like that anyway? Why do you need two sets of headlights? And why is there a 4x4 round plate on the roof when you can simply access from the back instead? It makes me conclude this is a MOC.