ATF: Allentown explosion that killed 3 was murder-suicide

Authorities say an explosion that killed three people in Allentown over the weekend was an intentional act and is now being investigated as a murder-suicide.

ATF officials announced Thursday afternoon that the explosion was an intentional act that was carried out by Jacob Schmoyer, 26, killing David Hallman 66, and Schmoyer's own two-year-old son Jonathan.

Investigators say they were able to retrieve four letters that appear to have been sent by Jacob Schmoyer to family members, and to the Allentown Police department. Some of the letters included specific details on the components and construction of the explosive device.

The letters also included indications that Schmoyer intended to target Hallman, and also intended to kill his son in the explosion. The first letter was received on Tuesday, and two more were received on Wednesday. Officials are still working to confirm the authenticity of the letters, but are "very confident" they were written and sent by Schmoyer.

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Investigators say Schmoyer also used the letters to explain that he no longer desired to "stick around," and admit to other criminal acts including petty thefts, burglaries.

Officials also released more information about the explosion itself. It was determined that Hallman was in the passenger seat of Schmoyer's car, and his son was in the back seat on the driver's side.

During the investigation, detectives found elements commonly used in homemade explosives. It was also confirmed that Schmoyer and Hallman knew each other prior to the incident.

Residents have been informed that there is no further danger to the public, and that Schmoyer is believed to have acted alone. FBI officials have also said rumors that Schmoyer was previously on a watch list were not true.

The investigation is ongoing as officials wait to receive more lab results.