Houston police Capt. Dwayne Ready says it's unclear if the unidentified man fatally shot himself or was killed by a Homeland Security agent who had confronted him.
Ready says the agent confronted the gunman after the man had fired one shot into the air around Thursday afternoon and had refused to drop his weapon.
Ready says the agent fired at the gunman at the same time as it appeared he was shooting himself.
Airport officials say the terminal remains closed but the rest of the airport is still operating.