If some aspects of the attack at the Pulse gay nightclub in Orlando Sunday morning appear either unique or unusual — the death toll was the highest for a single mass shooting in U.S. history and the Florida venue was known as a safe space for the lesbian, gay, bisexual and transgender community — there are other ways in which it had much in common with other high-profile mass killings in recent years.

Omar Mateen, the shooter slain by police, employed a military-style rifle that is similar to the weapon of choice of many mass shooters across the country.

And, like many of those killers, Mateen didn’t appear to have a problem getting his hands on one.

Nine days ago, Mateen, who had been investigated by the FBI on two occasions, walked into a gun store near his home in Port St. Lucie and bought an AR-15 assault-style rifle. The next day, he came back and picked up a Glock 17 pistol. Last Thursday, he returned for large magazines of ammunition so he could fire multiple rounds. Wielding the weapons just a few days later, Mateen entered the Pulse nightclub and opened fire, killing 49 people over several hours and wounding even more as law enforcement personnel scrambled outside to respond to and stop the carnage.

While assault rifles aren’t used as frequently in everyday gun crimes as other types of weapons, they are responsible for some of the highest death tolls in mass shootings.