A man told police he killed his two roommates because they were neo-Nazis who disrespected his recent conversion to Islam, and investigators found bomb-making materials and Nazi propaganda after he led them to the bodies.

Devon Arthurs, 18, told police he had until recently shared his roommates' neo-Nazi beliefs, but that he converted to Islam, according to court documents and a statement the Tampa Police Department released Monday.

Arthurs is being charged with two counts of first-degree murder, two counts of aggravated assault with intent to commit a felony and three counts of armed kidnapping. Court records did not list an attorney for him.

In the apartment with the victims' bodies on Friday, investigators found Nazi and white supremacist propaganda; a framed picture of Oklahoma City bomber Timothy McVeigh; and explosives and radioactive substances, according to the court documents.

They also found a fourth roommate, Brandon Russell, crying and standing outside the apartment's front door in his U.S. Army uniform.

"That's my roommate (Russell). He doesn't know what's going on and just found them like you guys did," Arthurs told the police officers, according to the report.

Federal agents arrested Russell, 21, on Saturday on charges related to the explosives.

The FBI said Russell "admitted to his neo-Nazi beliefs" and said he was a member of a group called Atomwaffen, which is German for "atomic weapon."

Major Caitlin Brown, spokeswoman for the Florida National Guard, confirmed Russell was a current member of the Florida National Guard. But she couldn't immediately provide any other information.

Arthurs started the chain of events on Friday when he held two customers and an employee hostage at gunpoint at a Tampa smoke shop, police said. He was complaining about the treatment of Muslims.

"He further informed all three victims that he was upset due to America bombing his Muslim countries," police Detective Kenneth Nightlinger wrote in his report.

Officers talked Arthurs into letting the hostages go and dropping his weapon, and took him into custody.

While in custody, police said Arthurs started talking about killing two people, and then he directed them to a condominium complex where the four roommates shared an apartment.

"I had to do it," Arthurs told police. "This wouldn't have had to happen if your country didn't bomb my country."

Inside the apartment, the officers found the bodies of 22-year-old Jeremy Himmelman and 18-year-old Andrew Oneschuk. Both had been shot.

Police called in the FBI and a bomb squad, which found enough explosives to constitute a bomb, according to federal agents.

At first, Russell told agents he kept the explosives from his days in an engineering club at the University of South Florida in 2013, and that he used the substances to boost homemade rockets. The agents wrote that the substance found was "too energetic and volatile for these types of uses."

Russell has been charged with possession of an unregistered destructive device and unlawful storage of explosive material. Court records did not list an attorney for him.

Andrew Auernheimer, a notorious computer hacker and internet troll, wrote a post about the killings for The Daily Stormer, a leading neo-Nazi website.

Auernheimer, known online as "weev," said in Sunday's post that he knew the shooting suspect and both of the shooting victims. He said he banned Arthurs from The Daily Stormer's Discord server, an online forum, for posting "Muslim terrorist propaganda" earlier this year.

"He came in to convert people to Islam," Auernheimer said during a telephone interview Monday. "It didn't work out very well for him."

Auernheimer described Himmelman and Oneschuk as "friends of friends" and said they belonged to the Atomwaffen group.

"Atomwaffen are a bunch of good dudes. They've posted tons of fliers with absolutely killer graphics at tons of universities over the years. They generally have a lot of fun and party," he wrote.

Dearen reported from Gainesville, Florida. Kunzelman from Baton Rouge, Louisiana.