Authorities in Las Vegas are looking for a "mystery woman" who was seen with gunman Stephen Paddock in the days before Sunday night's attack.
Claudia Cowan reported this morning that police believe someone else had to have known about Paddock's plot.
"Officials are trying to identify a mystery woman, not his girlfriend, as they try to build a timeline of his movements," she said from Las Vegas.
Officials do not know if the woman has any connection to the attack, NBC News reported.
Paddock's longtime girlfriend, Marilou Danley, was in the Philippines when the attack occurred. She returned to the U.S. earlier this week and immediately spoke to investigators.
Danley told investigators she had no clue Paddock was planning the mass murder. Paddock opened fire on a country music concert from the 32nd floor of the Mandalay Bay hotel, killing 58 and wounding more than 500.
Watch the full report above.