Trump rally shooter Thomas Crooks appears to have acted alone, used 'AR-style 556' rifle: FBI

Trump rally shooter Thomas Matthew Crooks appears to have acted as a lone wolf using an AR-style rifle that was purchased by his father, according to FBI officials.

In a call with reporters Sunday afternoon, FBI officials indicated they are still searching for a motive in the attack . The agency is acting as the lead federal law enforcement agency in the investigation of the shooting at Trump's Saturday evening Pennsylvania political rally.

"At present, we have not identified an ideology associated with the subject," said Kevin Rojek, a special agent in charge of the FBI's Pittsburgh field office. "At this time, the information that we have indicates that the shooter acted alone and that there are currently no public safety concerns."

Gunman used AR-style rifle purchased by father

Crooks used a legally-purchased "AR-style 556 rifle," according to Rojek, referring to a rifle that uses ammunition with a 5.56 mm diameter. Rojek said the weapon was located next to Crooks on the scene.

Another official on the call, who didn't identify himself when he spoke up about who purchased the weapon, said the FBI believes the weapon was bought by the shooter's father. Crooks was 20 years-old. He was shot to death by the Secret Service after the attack.

"We do not know specifically how he accessed the weapon and whether he took it without his father's knowledge," the official said.

Rojek said law enforcement is sending the rifle as well as Crooks' cell phone and other evidence, to the FBI lab in Quantico, Virginia "for processing and exploitation."

"We're in the process of searching his phone," Rojek said.

'Suspicious device' from car inspected by bomb technicians

Law enforcement also located "a suspicious device" when they searched the shooter's vehicle, according to Rojek. Bomb technicians inspected the device and rendered it safe.

He said law enforcement have now transported the device to the FBI lab in Quantico, Virginia for further analysis.

"I'm not in a position to provide any expertise on the specific components of any potential bombs or suspicious packages," Rojek added.

Investigation into possible domestic terrorism

The FBI is investigating the attack not just as an assassination attempt, but also as a potential act of domestic terrorism, according to Robert Wells, assistant director of the bureau's counterterrorism division. As a result, counterterrorism and criminal division investigators are working together to determine Crooks' motive.

"Our number one goal here is to identify the motive of the subject and determine whether he had any other associates or anyone else that was involved," Wells said.

So far, it appears Crooks was "a lone actor," according to Wells.

This article originally appeared on USA TODAY: Trump rally shooter Thomas Crooks appears to have acted alone, used 'AR-style 556' rifle: FBI