Looks like others are being investigated.
People other than the gunman are being investigated in Orlando shooting, U.S. Attorney Lee Bentley says - CNN.com
There are reports of survivors claiming there was more than one shooter. Some say FBI keeping lid on it
I was listening to live reports yesterday and several people interviewed reported multiple shooters as well as gun fire that simply did not end, that combined with the death/injured toll makes me think there were multiple shooters, guessing they were advancing and calling it out so one was shooting while the other was reloading.