The cop called 911 after the early Saturday hit-and-run near Canal Street and chased after the driver’s pickup truck along the West Side Highway until he lost sight of it, sources said.

Soon afterward, the truck smashed into a Dodge Challenger head-on, killing Walker, 38, and his cousin Rob McLaurin, who were celebrating Walker’s bachelor party, police and sources said.

The pickup truck’s driver took off after the crash, while police took a 22-year-old passenger into custody.