The Federal Bureau of Investigation has joined the hunt for a possible serial killer who is thought to be preying on store owners in Brooklyn.

The FBI is providing assistance to the New York City Police Department's Behavioral Analysis Unit, as NYPD investigators were looking to speak with four possible witnesses who were captured on surveillance video just after 6 p.m. Friday near the scene of the most recent killing.

Police say 78-year-old Vahidipour Rahmatollah died after he was shot times with a .22 caliber gun inside his She She Boutique on Flatbush Avenue.

Investigators say the same gun was used to kill two other shopkeepers.

NYPD officials also say the four people of interest are not necessarily suspects but may have seen something.

They are described as a man seen carrying a duffle bag, a woman wearing glasses and a neck scarf and long coat, a woman in a head scarf and green jacket and a man wearing a a bubble jacket.

Police Commissioner Ray Kelly said the NYPD wants to hear from anyone who was in the store on Friday.

"We're asking anyone who was a customer in that store on that Friday to come forward, even if it was in the morning hours, we believe that this murder took place after 4 p.m. But even if you were there in the morning we'd like to have people come forward and make themselves available to us," Kelly said.

Meantime, some Brooklyn lawmakers are reminding local store owners to be on alert.

"This person must be apprehended. We can't turn this into a fearful winter with an individual still out there with a 22-automatic weapon causing havoc on the people of this borough," said State Senator Eric Adams.

"We know he's targeting places without cameras. This is information we need to get out there so we can keep the number at three," said City Councilman Jumaane Williams.

Ballistics evidence confirms the same gun was used to kill Bay Ridge shop owner Mohamed Gebeli on July 6 and Bensonhurst store owner Isaac Kadare on August 2.

Police are offering $22,000 rewards in each case for information leading to the killer or killers.

Anyone with information on the shootings should contact the Crime Stoppers hotline at 1-800-577-TIPS, or text CRIMES and then enter TIP577, or visit www.nypdcrimestoppers.com.