ROME - Italian prosecutors placed the captain of the Jolly Nero cargo ship under investigation Wednesday for alleged manslaughter after his vessel slammed into the dock at Genoa's busy port and toppled the control tower into the harbor, killing at least seven people.

As rescue teams in diving suits searched for two missing people, officials began piecing together how the 40,000-ton container ship could have sideswiped the port's control tower when conditions were "perfect" Tuesday night.

The crash occurred about 11 p.m. as the 784-foot-long Jolly Nero was backing out of Genoa's port accompanied by two tugboats and with a harbor pilot on its bridge. At the same time, a shift change was taking place among employees at the control tower, meaning more people were in the building than usual.

"This event is unbelievable because we had the best weather navigation conditions," said Luigi Merlo, president of Genoa's port authority.

Transport Minister Maurizio Lupi told Parliament that given the weather conditions, possible causes of the crash could include an engine malfunction or problems with the cables between the container ship and the tugs guiding it.

The Jolly Nero's captain, Roberto Paoloni, and the harbor pilot on board were placed under investigation for alleged manslaughter, Genoa prosecutor Michele di Lecce told reporters. He said other accusations were possible.

Firefighter spokesman Luca Cari confirmed that seven people were killed, saying rescue crews recovered several bodies near the tower's submerged elevator. There were fears the two still missing might be trapped inside the elevator.

The dead included three coast guard officials in the tower at the time of the crash, a port captain, and a tugboat operator, said Cmdr. Filippo Marini, a coast guard spokesman.