New York Deputy Commissioner Paul Browne said it's not clear if the three murders were perpetrated by the same shooter or shooters, though ballistics tests indicate the shell casing came from the same .22-caliber gun.
Even if it was the same shooter, Browne said, "it's too soon to tell" if the suspect or suspects should be classified as a serial killer or killers, CNN reported Sunday.
"There are similar things in each case, but that determination hasn't been made yet," Browne added.
The FBI defines a serial killings as "three or more killings ... having common characteristics such as to suggest the reasonable possibility that the crimes were committed by the same actor or actors."
The most recent victim was Vahidipour Rahmatollah, 78, who was found shot three times in the torso and head Friday at his clothing store in Brooklyn.
Isaac Kadare, 59, was shot in the head in his discount store Aug. 3, and Mohammed Gebeli, 65, was shot in the head and stabbed in the neck in his clothing shop July 6, both in Brooklyn.
Money was missing from the stores in both the Gebeli and Kadare murders, though police have yet to determine if anything was missing from Rahmatollah's shop, CNN reported.