Austrian police discovered Ghanem's body in the Danube River in April. There were no signs of foul play.
The prosecutor's office in Vienna said Ghanem likely died from heart failure after falling into the river. There were no harmful substances discovered in his blood stream, reports Bloomberg News.
It wasn't clear where Ghanem was working at the time, though he had served as an official at the Organization of Petroleum Exporting Countries during his tenure in the government of Moammar Gadhafi. OPEC has headquarters in Vienna.
Ghanem defected from the Gadhafi government during the civil war last March. He served in Libya as the prime minister from 2003-06 and as oil minister until his defection.
The case isn't closed, however, as authorities are still investigating the circumstances surrounding his death.