Here are the TSA's rules for transporting guns and ammunition through US airports

A mass shooting at Florida's Fort Lauderdale-Hollywood airport Friday left five dead and dozens wounded, and the suspect apparently kept the gun used in the attack in his checked luggage.

The TSA allows passengers to carry firearm while traveling through US airports, but strict rules govern how passengers are supposed to handle them.

Firearms must remain unloaded and kept "in a locked hard-sided container as checked baggage only," according to the Transportation Security Administration's website.

The TSA also points out locked cases cannot be easily opened and "only the passenger should retain the key or combination to the lock."

In 2015, the TSA discovered 2,653 firearms in carry-on bags and 2,198 of those — that's 80 percent — were loaded. The number was a 20 percent increase over 2014, according to the TSA's blog.The agency has not yet issued its annual review for 2016, but has been documenting firearms found in carry-on bags weekly.

The suspect, 26-year-old Esteban Santiago, allegedly loaded the gun in a bathroom before opening fire in the baggage claim area of Terminal 2, Broward County Commissioner Chip LaMarca wrote on Facebook. Santiago is now in federal custody.

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