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ALLENTOWN, Pa. (CBS/AP) — Authorities revealed Thursday that a man intentionally caused a car explosion that killed three people, including his toddler son, in a murder-suicide in Allentown last Saturday night.

Don Robinson, special agent in charge of the ATF Philadelphia Field Division, said in a news conference that 26-year-old Jacob Schmoyer planted the homemade explosive device in his car that killed himself, his 2-year-old son Jonathan “JJ” Schmoyer, and a friend, 66-year-old David Hallman.

“This was an intentional act by Jacob Schmoyer,” said Robinson.

Robinson revealed that Schmoyer sent letters to his family members and the Allentown Police Department prior to the car explosion. The letters indicated that Schmoyer took the blame for the blast and that he intended to target his son and Hallman. The letters also indicated the components and materials used in the homemade bomb.

“We are very confident at this point it was Mr. Schmoyer. The crux of the letters, he was very unhappy with his life,” said Robinson.

Officials say Schmoyer had the explosive device in the front console, and his 2-year-old son in the back seat, when he lured Hallman to get in the car. He then detonated the homemade explosive device.

The blast scattered debris and body parts over several city blocks.

“What happened here in Allentown on Saturday night, was nothing short of a nightmare,” said assistant U.S. Attorney John Gallagher.

Authorities say surveillance video of the bombing shows other people walking by moments before the blast. They say it’s a miracle more people weren’t killed.

Investigators say Schmoyer acted alone and there is no threat to the public.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)