Orlando gunman 'was regular at gay nightclub'

The FBI is investigating reports that Orlando gunman Omar Mateen was a regular at the gay nightclub where he killed 49 people in America's worst mass shooting.

A number of possible explanations and motives for the bloodbath have emerged, with Mateen having professed allegiance to the Islamic State group (IS), his ex-wife saying he was mentally ill, and others suggesting he was driven by a hatred of gays.