This mission is given by Rocco.
"Alright Joe, got somethin for ya' that's a little more... delicate. Got word one of our guys is lookin' to get himself promoted. Sonnavabitch is ready to make a move on Falcone. I need this asshole dead, today. Guy is well liked, don't think anyone, even Falcone will believe it. You take him out, but you make sure it don't get back to anyone, especially me. I got somethin' special for ya' to pull off the job. And Joe, you better not fucking miss."
This is a quick and easy assassination. Start the mission and drive around the corner to the South Millville Industrial Estate where the hit will take place. Run up the stairs and walk out onto the platform where you'll find a K98 Rifle rifle leaning up against the railing. Even if you already have that weapon, you still have to pick it up to progress forward.
With the rifle in hand, look down and a group of thugs will begin to gather below. The target will be the last one out and have a large green arrow above him. When he stops walking, take careful aim and kill him. When he's dead you can either stay and kill his companions for extra points or just run back down the stairs to the safe zone below and end the mission.