US investigators are trying to determine whether conspiracy theories motivated the suspect in the Christmas Day bombing in Nashville.
Police are trying to figure out why Anthony Quinn Warner detonated a bomb that killed himself and injured three others.
The suspect is said to have expressed support for unfounded theories and would camp out to hunt aliens.
Police are also probing whether he believed 5G conspiracy theories.
The 63-year-old's criminal record only consisted of a 1978 marijuana-related charge.
The suspect had reportedly made statements about a "lizard people" conspiracy theory which claims politicians and celebrities such as Justin Bieber and the Obamas are lizards with alien origins which are now taking over the world.
On Christmas Day, a van blew up outside a building belonging to the telecoms giant AT&T, disrupting communications systems in Tennessee and four other states.
Warner, who worked in IT, was the only person killed in the blast.
On Wednesday it was revealed that the girlfriend of the suspect, Pamela Perry, told police last year that he was making explosives in a trailer at his home.
Earlier in the week investigators said that Warner was "not on our radar".
Following Ms Perry's comments, officers were sent to Warner's home but he did not answer, and the officers left because "they saw no evidence of a crime and had no authority to enter".