Several officers, including Detective Thomas Redmond, watched the 17-year-old walk away from his Lambertville home early Sunday carrying a bucket before he approached Redmond's unmarked vehicle.
Police say the teen unscrewed the gas cap and started siphoning the fuel before Redmond got out of the car and chased him.
Authorities say the teen later admitted to the two arsons as well as three other arsons in 2006.