Washington (CNN) Attorney General Jeff Sessions said Thursday that law enforcement "must do better" to prevent mass shootings in the wake of the massacre at a Florida high school.

"It is just too often the case that the perpetrators have given signals in advance," Sessions said in a speech to the Major County Sheriffs' Association.

"We've had advance indications and perhaps we haven't been effective enough in intervening immediately to deal with that. I suspect it appears that we've seen that again in this case."

He told the group of sheriffs gathered in Washington that "we cannot arrest everybody that somebody thinks is dangerous."

"But I think we can and must do better. We owe it to every one of those kids crying outside their school yesterday and all those who never made it out," Sessions said. "Our hearts are hurting today."

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