Authorities say after a nearly 19-hour standoff, SWAT teams entered the first-floor building in Herkimer around 8 a.m. where Kurt Myers, 64, had been holed up. Myers opened fire through a door at officers, killing an FBI dog, police said.
Officers returned fire, killing Myers. No officers were hurt in the incident.
The shootout ended a nearly 24-hour ordeal that began at a barbershop in Mohawk around the corner from his apartment. Police say Myers sauntered into the barbershop, coolly asked if the man cutting hair remembered him and then opened fire with a shotgun, killing two customers and wounding two others. The fatal victims were identified as Harry Montgomery, 68, and Michael Ransear, 57.
Investigators say Myers then drove to Gaffey's Fast Lube in nearby Herkimer and gunned down two more people, identified as Michael Renshaw and Thomas Stefka.
The motive behind the shootings remains unclear.
"He's apparently a loner," State police Superintendent Joseph D'Amico said. "He didn't have a lot of contact with his family. The few people we did find that were relatives - we interviewed some neighbors - nobody could offer any explanation."
When police were searching for Myers on Wednesday, he allegedly opened fire on officers at 1:30 p.m. They surrounded an abandoned bar called Glory Days where they believed he was hiding.
The two villages are about 65 miles east of Syracuse on opposite sides of the Mohawk River, in a region known as the Mohawk Valley.
The Associated Press contributed to this report.