You can get this even easier. Just go to the docks at Drassanes, it's on the bottom of the map, somewhat in the middle. There's a long dock there, with a small walkway on the side of it. Just stand in front of the dock, and shoot a few people. Then police will start arriving, shoot some of them, and then quickly run onto the small walkway on the side of the dock. Stay at the very end of it, and wait for 5 minutes. One of the easiest 25g ever ;-)