The gun used to kill nine people in less than one minute during the Dayton shooting rampage was a tricked-out AR-15 style rifle that was “obtained legally,” authorities said Sunday — as they revealed the killer also brought a shotgun to the scene, but left it in his car.

During a press conference, police displayed a photo of the rifle Connor Betts used, which was also equipped with a “double-drum” magazine that could hold 100 rounds.

“It is certain dozens [of rounds] were fired,” said Dayton Police Chief Richard Biehl.

Betts, 24, obtained the gun legally, he said.

“There’s nothing in his history that would have precluded him from buying the firearm,” Biehl said, adding that there was “nothing to suggest the magazine is illegal” either.

The rifle was ordered online from Texas and “transferred at an area firearms dealer,” Dayton said.

Authorities also recovered a shotgun from the car Betts arrived at the scene in, the chief said. That gun was also purchased legally.