The FBI has unlocked a Samsung phone belonging to Connor Betts, the gunman who killed nine people in a mass shooting in Dayton, Ohio on Sunday, a Senate Democratic source told CBS News on Thursday. Betts, however, had multiple phones, and it's not clear whether the FBI has been able to unlock all of them.

The source said the the FBI briefed the Democratic Caucus on its investigation into Betts on a conference call. Lawmakers were told that the bureau is still working on gathering all of Betts' social media.

Betts, the FBI said on the call, legally purchased the gun used in the massacre, a .223-caliber assault-style weapon, but he obtained the double-drum ammunition magazine, which has a 100-round capacity, from a friend.

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On Sunday, Betts opened fire in a popular nightlife district in Ohio, killing nine and injuring 27 others, before he was killed by police, authorities said. The rampage, which lasted under one minute, was the second mass shooting in the U.S. in less than 24 hours.

Democratic lawmakers have called on Senate Majority Leader Mitch McConnell to convene an emergency session to address recent mass shootings, but McConnell has declined to do so. He did say Thursday that gun control measures would be on the table when Congress reconvenes in September.