Carrie Underwood

WHAT'S HAPPENING: Las Vegas hotel gunman's motive a mystery

The motive behind the deadliest mass shooting in modern U.S. history remained a mystery Monday as police sought to learn more about the apparent "lone wolf" gunman who opened fire on thousands of concertgoers from the 32nd floor of a Las Vegas hotel.

At least 59 people were killed and hundreds more were injured in the shooting, which happened during a performance by country music star Jason Aldean Sunday night at the Route 91 Harvest Festival. The gunman hammered out a window at the Mandalay Bay Hotel and Casino and began firing with a cache of weapons . Authorities who stormed the suspect's room found that he had killed himself.

Here are some things happening in...