Two rival gangsters team up to track down a cop, while one wants him dead, the other wants him alive.

Appreciate your comment a lot guys. This website has really helped me. I got the idea 3 days ago and just posted it. I will work on the Motivation, stakes and develop the story. .

I think it starts off very well and I wouldn't change the first part, but it does need more info to sweeten the pot and give us more insight on the story itself.
But all in all it's a start.

I haven't seen anything like this before and I love the fact that it flips what we usually get to see.

I also do like 'rival' as it provides the main conflict in the film. It sounds like it could be a 'buddy' movie where they overcome their differences in the course of the journey.

What is missing are the stakes. What do the gangsters have to win or lose? This will probably come out when you give us the motivation. Either way, we need more.

This is pitched as a dual-journey movie. They are hard to pull off if you don't have a lot of experience... (I've written something about this here: http://bit.ly/ONEhero) Perhaps the story can be told from the POV of one of them.