An Allentown man purposefully exploded a device while he was in a car with his toddler son and friend Saturday night in the city, authorities said Thursday.

Jacob Schmoyer is accused of using the device with two different explosives on Saturday night while he was parked in his car with his 2-year-old son Jonathan and friend David Hallman in the 700 block of West Turner Street in Allentown.

Schmoyer used a homemade explosive, officials said. All three were killed.

"We are confident Schmoyer acted alone. He is not involved in any groups," said Don Robinson, the ATF special agent in charge. "We are confident this was an isolated incident."

Videos from that night showed the 66-year-old Hallman, who lived nearby, got into the car seconds before the blast, U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives Special Agent Charlene Hennessy said.

Robinson said Schmoyer "lured" Hallman into the vehicle.

"(Schmoyer) was unhappy with himself...there was a lot of hatred there," Robinson said.

Graphic videos of the blast aftermath, which were posted on social media, showed body parts and car pieces strewn around the burning vehicle.

Robinson said Schmoyer sent four letters, three to family members and one to Allentown police. The first letter was received on Tuesday, and the other three were received on Wednesday.

Screenshots of purported posts from Schmoyer's Facebook page eight years ago showed he discussed using explosive compounds. Asked about possible social media posts, Robinson said there was not a lot of social media content in the case.

Officials called it a grisly scene that "no one should have to see."

Officials released two photos of Schmoyer's destroyed vehicle, which investigators pieced back together as part of the investigation.

Hallman's dog, which news outlets have said is a Jack Russell Terrier named Skippy, remained in Hallman's nearby car during the explosion in the vehicle Schmoyer had parked, Hennessy wrote Wednesday night. The dog was later treated for minor injuries and returned to family, she added.

District Attorney Jim Martin previously called the blast a "criminal incident," and officials said the perpetrator was killed in the blast.

Turner Street reopened Thursday.

Allentown police Chief Tony Alsleben said if anyone finds any items that might be related to the blast to not touch the item and immediately call police at 610-437-7751.

Sarah Cassi may be reached at scassi@lehighvalleylive.com. Follow her on Twitter @SarahCassi. Find lehighvalleylive.com on Facebook.