Matthew Livelsberger, a 37-year-old Green Beret from Colorado Springs, Colorado, also wrote in notes he left on his cellphone that he needed to “cleanse” his mind “of the brothers I’ve lost and relieve myself of the burden of the lives I took.” Livelsberger served in the Army since 2006 and deployed twice to Afghanistan.

“This was not a terrorist attack, it was a wake up call. Americans only pay attention to spectacles and violence. What better way to get my point across than a stunt with fireworks and explosives,” Livelsberger wrote in one letter found by authorities and released Friday.