The United States Coast Guard will on Tuesday start interviewing the crew of a Philippines-flagged container ship which collided with a U.S. warship in Japanese waters killing seven American sailors. The U.S. coast guard investigation is one several into the incident on Saturday involving the guided missile destroyer USS Fitzgerald and the much larger ACX Crystal. The cause of the collision at night and in clear weather is not known. "We are scheduled to interview the crew members," said U.S. Lieutenant Scott Carr told Reuters, referring the crew of the merchant ship.