News of the legal purchases comes as officials confirmed that Mateen had been interviewed three times by the FBI in the years leading up to the shooting because his name came up in connection to two different cases. Such information would not show up in a background check because both cases were closed.
Law enforcement sources confirmed that Mateen was on the FBI's radar but not necessarily on a watch list. But even appearing on the list wouldn't have necessarily prevented him from obtaining weapons.
"Being on the watch list is not in itself disqualifying, under law. The disqualifying elements of the investigation may be classified," ABC News consultant and former acting Homeland Security undersecretary John Cohen said.
According to Florida law, there is a mandatory three-day waiting period for handgun purchases, but no permit, registration or licensing is needed to buy or own rifles, shotguns or handguns. A permit is needed, however, to carry a handgun.
As a state, Florida is said to have relatively lax gun laws.