Investigators still trying to determine motive more than a day after assassination attempt on Trump

More than 24 hours after the assassination attempt on former President Donald Trump, a motive for the 20-year-old shooter's actions has not been identified, the FBI said Sunday.

Little is known about the shooter, Thomas Matthew Crooks, although investigators stressed the investigation is in its early stages, and they are still seeking to gain access to his cellphone.

The shooter acted alone, but investigators are still working to determine "if there were any co-conspirators associated with this attack," the bureau said in a statement. "At this time, there are no current public safety concerns," it added. There were no current indications that Crooks had mental health issues, officials said.

Crooks fired several shots from a nearby rooftop during a Trump rally in Butler, Pennsylvania, narrowly missing the former president, killing one rally attendee and injuring two more before he was killed by at least one Secret Service sharpshooter.Corey Comperatore, 50, a former chief of the Buffalo Township Volunteer Fire Company, was identified as the person killed. The two other victims were stable.

Trump, who ducked and surfaced with a bloodied face, said he was shot in the ear and described feeling a “bullet ripping through the skin.” He arrived in Milwaukee Sunday night for the Republican National Convention.

The shooting is being investigated "as an assassination attempt and potential domestic terrorism," the FBI statement said.

The FBI also said it had obtained Crooks' phone and searched his home and vehicle. In a press call on Sunday, an official said the FBI had shipped the phone off to the FBI lab in Quantico, Virginia, to try to gain access to it.

The semiautomatic rifle used in the shooting had been purchased legally