EXCLUSIVE

11:25 AM PT -- Oman police say Avicii's body will be flown home to Sweden this week. Still no word on the cause of his death.

One of Avicii's family members is on the ground in Oman leading the charge to find out what killed the world famous DJ ... TMZ has learned.

Sources in Oman tell us Avicii's older brother, David Bergling, checked into an upscale hotel in the capital city of Muscat on Friday evening ... hours after Avicii was found dead. We're told the hotel where he's staying is about 15 minutes away from Muscat Hills -- the resort where Avicii had been vacationing.

As we showed you, the EDM superstar posed for several photos with fans at the resort, and witnesses say he appeared to be in good spirits during his time there.

According to reports in Avicii's native Sweden, he had checked out of Muscat Hills sometime last week. One of the things David is likely looking into is exactly where his brother and a small group of friends went in the days leading up to his death.