The FBI had a sit-down interview with another member of the mosque that was attended by Orlando killer Omar Mateen and a suicide bomber in Syria both attended service. Via the NY Post: 
In what was the first such known interview in connection with the nightclub shooting, two federal agents met with the man at the mosque for about 30 minutes ahead of Friday prayers, according to Omar Saleh, a lawyer for the Council of American-Islamic Relations who sat in on the session.
“We were meeting with some agents,” Saleh told Reuters, declining to identify the person interviewed. “They were asking questions relative to the incident that happened on Sunday.”