A Tunisian judge held seven crew members of a commercial ship that drowned off the coast of Gabes earlier this month, according to a judicial official, as police examined if the ship was deliberately sunk.

The Xelo, a ship carrying up to 1,000 tons of oil from Equatorial Guinea to Malta, sank last month, according to Tunisian officials, and all seven crew members were rescued by the Tunisian navy.

Officials later said a specialized diving team sent to counter a potential environmental disaster found the ship cargo did not contain fuel, but rather was empty.

“The investigative judge issued a detention decision against the ship’s crew,” said Mohamed Karay, a spokesman for the Gabes court.

Karay had previously said an investigation was being conducted to determine if the ship sank under normal circumstances or was sank to obtain compensation from insurance companies, and to look into the possibility of oil smuggling.

The crew of the ship were four Turks, two Azerbaijanis and one from Georgia.

The crew claimed the ship’s route documentation had been lost, and that there was a conflict in the information they provided, Karay said.

Reuters could not immediately contact the crew, the ship owner or their legal representatives.