Sen. James Lankford (R-Okla.) said Sunday he supports improving the background check system for buying a weapon, but said he doesn't think it needs to be harder to buy an AR-15, which was used in a Florida high school shooting last week.

"I actually don't think it should be. I think what should be is difficult for any person with any kind of criminal background history, domestic violence, mental instability, all those things, regardless. I don't care whether they're buying a .22 pistol or an AR-15," Lankford said on NBC's "Meet The Press."

"The problem is not owning an AR-15, it's the person that owns it," Lankford added.

Nikolas Cruz, 19, faces 17 counts of premeditated murder after officials say he opened fire at Marjory Stoneman Douglas High School in Parkland, Fla., last Wednesday, killing 17 and wounding more than a dozen others. He reportedly used an AR-15 that he was able to purchase legally.

Cruz had been flagged as a threat after he was kicked out of school.

The FBI acknowledged it failed to properly act on a tip it received about Cruz's erratic behavior and violent threats.

Lankford said on Sunday he supports legislation to improve the National Instant Criminal Background Check System and ensure it is fully up to date.

He said he supports slowing down weapons purchases for buyers who show "basic warning signs," but noted in Cruz was able to buy a firearm anyway.

"All the warning signs were there, the community did all the things the community should do to be able to engage, they saw something they said something and nothing was done," Lankford said.