Last Updated Oct 4, 2017 1:13 PM EDT
MESQUITE, Nevada – Guns & Guitars general manager Christopher Sullivan told CBS News he solda rifle on Sept. 28, the same day police say Paddock checked into the Mandalay Bay hotel.
"I was ill. It made me physically ill to think that we had interacted with him and he had committed such a tragedy," Sullivan said.
"Feel any guilt about what happened?" CBS News correspondent DeMarco Morgan asked.
"I don't. No," Sullivan said. "We do everything right. ... We can't control what someone does once they leave this store."
Sullivan said Paddock had been a customer of Guns & Guitars for about a year, and in that time the shop sold him five firearms.
"Just knowing that this may have been his last stop before heading to Las Vegas, does that make you feel some type of way? Sort of responsible?" Morgan asked.
"This morning over coffee I was having a moment in myself thinking that I may have very well been the last person to shake hands with that man,'" Sullivan said.
Paddock fired into a Las Vegas crowd Sunday night in what sounded like automatic rounds. The ATF said Paddock had 24 guns in his hotel room, and 12 of them had bump fire stocks. The legal devices are attached to the back of rifles and allow squeezed triggers to slide back and forth more quickly, simulating automatic fire.
"These bump stocks are basically a work-around that allow people to take a gun that's perfectly legal and turn them into something equivalent to a machine gun," UCLA law professor Adam Winkler said.
Winkler said if there is gun reform, it could involve regulation of modification devices like bump fire stocks.
"I think that's the kind of regulation that the NRA may support," Winkler said. "There's a broad consensus even among gun owners that people shouldn't have access to automatic-fire weapons. … Banning these devices is a way of banning automatic fire weapons."
Guns & Guitars tell CBS News it did not sell Paddock any automatic weapons, ammunition or bump fire stocks. Another store in north Las Vegas where Paddock purchased several weapons earlier this year tells us it also ran all proper background checks and did not sell Paddock any automatic weapons.