The gunman who killed nine and wounded at least 27 in Dayton, Ohio, used an AR-15 style pistol in his attack, according to police, a smaller variation on the popular gun that has been used in many of the deadliest mass shootings.

The pistol, which has grown in popularity as major gun manufacturers started promoting it in the past few years, has a shorter barrel than an AR-style rifle, but it fires the same types of bullets and uses the same magazines.

It appears to be the first time that an AR-style pistol has been used in a mass shooting, according to law-enforcement officials.

The Dayton shooter attached a 100-round drum magazine to his pistol and fired off at least 41 rounds in less than a minute before he was gunned down by police.

“It was modified, in essence, to act as a rifle,” Dayton police Chief Richard Biehl said at a press conference Monday. “And to avoid any legal prohibitions.”