The captain is suspected of causing death on probable cause following the accident at the end of July, when a merchant ship collided with a pleasure boat. The pilot who was on board at the time of the accident is also a suspect.
"Currently, the suspicions of crime are equally strong against the captain and the pilot," said prosecutor James von Reis in a press release.
They have both been confronted with radar sequences from the incident that were saved in the cargo ship's so-called "black box".
"Both have admitted that you can see clear radar echoes from both pleasure boats in good time, both the one that was hit and sank and the accompanying boat that was a little ahead. But that they have not noticed this in real time," says von Reis and adds:
"If they had only done so, measures would have been taken at Misje Verde to avoid a collision."
The captain's defense attorneys had previously announced that they would oppose extending the detention and that the captain denies any wrongdoing. The pilot, who was not detained, has also denied any wrongdoing.
Of the four people on the pleasure boat, two died, a woman and a child.
