Mohammod Youssuf Abdulazeez, the man who killed five people at two U.S. military facilities in Chattanooga, Tennessee last week, was critical of tactics employed by the Islamic State militant group, his friend said Monday. Abdulazeez was killed last Thursday in a shootout with local police after he targeted military personnel with at least three firearms.

Abdulazeez told his friend James Petty that the Islamic State, also known as ISIS or ISIL, was “doing wrong” through its use of violence,” Petty told CNN Monday. Abdulazeez also described ISIS as a “stupid group” whose actions were “completely against Islam,” Petty added.

Petty said Abdulazeez trained him to use an AR-15 assault rifle, CNN reported. Abdulazeez carried at least two “long guns” and one pistol during the attack, Ed Reinhold, the FBI Special Agent in Charge of the investigation into the Chattanooga shooting, said at a press conference last Friday.

Federal officials have so far declined to speculate on a possible motive for Abdulazeez’s actions. The 24-year-old was described as a well-liked former high school wrestler who obtained an engineering degree from the University of Tennessee-Chattanooga. Authorities said they found no initial evidence to suggest Abdulazeez was tied to the Islamic State or any other foreign group, but vowed to investigate a trip he took last year to the Middle East.

Investigators had purportedly obtained several of Abdulazeez’s personal writings by Monday, some of which discussed his disapproval with the United States’ war on terror, CNN reported. A representative of Abdulazeez’s family said the Chattanooga shooter expressed suicidal urges as early as 2013 and wrote about “becoming a martyr” after he lost his job, ABC News reported. Moreover, Abdulazeez was said to have abused various types of drugs, both prescription and recreational, and to have been in significant financial debt at the time of his death.

In a statement released last Saturday, Abdulazeez’s family expressed grief and sorrow over his actions in Chattanooga.

“There are no words to describe our shock, horror, and grief. The person who committed this horrible crime was not the son we knew and loved,” the statement said, according to NBC News. “For many years, our son suffered from depression. It grieves us beyond belief to know that his pain found its expression in this heinous act of violence.”