While law enforcement said at a press conference late Saturday that they believe they know who carried out the shooting, they are still not naming the individual.

Officials said they are also doing DNA testing, because the suspected shooter did not have ID.

"It's a matter of doing biometric confirmations," FBI Special Agent in Charge Kevin Rojek said. "So, there was no identification on the individual, for example, so we're looking at photographs right now and we're trying to run his DNA and get biometric confirmation."

The shooter's name will be released once there is an official confirmation, he said.

7:39

Gunman at Trump rally tentatively identified, FBI says

Law enforcement officials held a press conference after deadly gunfire erupted at a Trump campaign rally in Butler, Pennsylvania.

Trump arrives at Newark Liberty International Airport just after midnight early Sunday.

He arrived in Newark about six hours after the shooting took place.

Trump had been scheduled to spend the night at his club in Bedminster prior to the shooting taking place.

Authorities believe they have an identification on the suspected shooter, but are not yet releasing a name "as it is a very sensitive point in the investigation," according to a law enforcement source.

Early indication is that this is a lone wolf, the source said, but the situation is fluid and the investigators want to be absolutely certain that this person had no support and that no one knew what was coming.

The gunman opened fire with a rifle from the roof of a building about 200 to 300 yards away from the stage where Trump was speaking. A U.S. Secret Service counter-sniper team immediately killed the individual.

Trump left the Butler, Pennsylvania, area just after 11 p.m., according to Gov. Josh Shapiro.

"Under the protection of US Secret Service and with the assistance of the Pennsylvania State Police, former President Trump has now left the Butler area," Shapiro said. "Lori and I are thankful that his team reports that he is fine and we continue to wish him a full and speedy recovery."

The former president left the area about five hours after the shooting took place.

Trump's plane took off from Pittsburgh, but a destination was not released.