BROOKLYN - The reward for information on the murders of three shopkeepers by a possible serial killer has been upped to $40,000.

Surveillance video was released earlier showing a balding, middle-aged man wearing an overcoat and carrying a duffel bag. Authorities say the video was captured about a block from the most recent murder.

Police say 78-year-old Rahmatollah Vahidipour was shot in the head and torso three times at his Flatbush Avenue boutique Friday evening. Investigators linked the gun used in the shooting to the murder of two other Brooklyn shopkeepers over the summer.

All three shopkeepers were of Middle Eastern descent. Police say the NYPD Hate Crime Task Force has also opened its own investigation.

Investigators say they are also looking to question an older woman who may have witnessed Friday's killing. Two other possible witnesses have been questioned and released.

Police are asking anyone with information to call Crime Stoppers at 1-800-577-TIPS.