Italian authorities said on Saturday that they had opened a manslaughter investigation into the sinking of the Bayesian luxury yacht, but that they had not yet zeroed in on any potential suspects.

The sleek, $40 million sailing boat went down fast in a storm off Sicily’s coast on Monday morning, killing Michael Lynch, a British tech billionaire; his teenage daughter, Hannah; four of his friends; and one member of the crew. The captain escaped on a lifeboat with 14 others.

On Saturday, Ambrogio Cartosio, the prosecutor in charge of the case, said at a news conference that it was “plausible” crimes were committed during the accident.

“There could be responsibilities of the captain only,” he said. “There could be responsibilities of the whole crew. There could be responsibilities of the boat makers. Or there could be responsibilities of those who were in charge of surveilling the boat.”

Here is what the authorities said on Saturday:

• It will be difficult to determine the cause of the sinking until the yacht is brought to the surface and inspected, which could take weeks.

• Five bodies were found in the same cabin.

• The yacht sank at an angle, with the stern — where the heavy engine is situated — having gone down first.

• The captain and the crew, who have been holed up in a Sicilian hotel with other survivors, are allowed to leave Italy. But prosecutors said that they still want to ask them more questions.

• The authorities did not perform alcohol or drug tests on the captain or the crew.

• The authorities would not comment on whether hatches on the deck had been left open, which would have allowed water to pour in during the yacht’s sinking.

• In addition to possible manslaughter charges, the authorities are also investigating the possibility of a negligently caused shipwreck, a crime that carries up to several years in prison upon conviction.

Investigators said they were focusing on why the 184-foot-long Bayesian, which was built in 2008, went down so quickly, especially when other yachts nearby weathered the storm.

Executives at the company that built the boat have said there is nothing faulty with the design of the yacht and have tried to shift the blame to the crew.

At the news conference on Saturday, the authorities were asked why the captain, James Cutfield, an experienced sailor, left the sinking boat while some passengers were still on board.

“The investigations are also focusing on this,” said Raffaele Cammarano, another prosecutor. But he added that the witnesses they had spoken to said that “the event was really, really sudden.”

Some people who were along the Sicilian coast at the time of the sinking described seeing waterspouts, which are vicious funnels of water and wind that sweep across a body of water during thunderstorms. But on Saturday, Italian authorities said they believed it was more likely that a downburst occurred at the time of the accident.

A downburst is a blast of powerful wind that comes surging down from the sky during thunderstorms. The Italian authorities said that extreme weather was “one of the main elements” of their investigation, but added that they were still at the early stages of their inquiry and that they did not want to “play the probability game.”

The rescuers found the bodies of five passengers in one cabin, which was on the left side of yacht. The yacht was found lying on its right side at the bottom of a bay, in about 160 feet of water. The authorities said the passengers who died were most likely trying to flee to the higher side of the boat and were probably sleeping when the accident happened.

The authorities said that they were not certain whether a black box existed and that the hull was still being searched.

Mr. Cartosio would not comment directly on the actions of the crew, but said that it would be “even more painful” if “the sinking was caused by behaviors that were not perfectly in order with the responsibilities that each person must have in the management of navigation.”

But he added that “this is just, in fact, the beginning of an inquiry.”