Revealing mistake: As the Jackal is opening up his large weapon onto Lemont and Lemont's car, there is a close up of the car's fender as bullet holes get riddled through it. Just before the third hole appears, you can see an outline in the paint where a patch is covering one of the special effects explosive charges rigged to blow the hole open. (01:01:05)
Answer: He probably used a window punch. It's a small device used for breaking a car window in the event of an emergency. A recessed metal pin is within a plastic housing. When pressed against the window, the pin's pointed end pushes into the window, shattering it. I carry such a device on my key chain.
raywest ★