New York (CNN) -- A shooting and subsequent gun battle at the Empire State Building in New York killed two people and wounded at least nine others Friday, authorities said.

The shooter was one of the two killed, investigators said. They identified him as Jeffrey Johnson, 53, who was laid off last year and apparently killed a former co-worker Friday morning.

A construction worker followed the suspect and alerted officers. The suspect, using a .45-caliber semi-automatic handgun, then fired on police and they returned fire, killing him, said Police Commissioner Ray Kelly.

Most of the injuries apparently occurred during the exchange of gunfire, and some may have been hit by shots fired by police officers, Mayor Michael Bloomberg said.

The White House said top aides told President Barack Obama about the shooting around 9:30 a.m. The shooting does not appear to be linked to terrorism, authorities said.

From CNN.com

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