BRANSON, Mo. -- A federal criminal investigation into a deadly duck boat sinking on a Missouri lake was initiated after the U.S. Coast Guard determined the 17 deaths resulted from "misconduct, negligence or inattention to the duties" by the captain of the duck boat, according to a court document filed Wednesday.
The new investigation also is looking at another duck boat captain and officials at the company that operates the tourist ride, the court document says.
There are several investigations into the July 19 incident, including the state of Missouri, which is also looking into criminal liability, and the National Transportation Safety Board, which is trying to determine what caused the sinking.
Survivors of some of the people who died are, in four cases, suing Ripley Entertainment, which runs the duck boat tours called Ride the Ducks Branson.
On Wednesday, the U.S. government attached a motion to the civil cases, asking that a court rule that federal investigators be allowed first to talk to the pertinent witnesses and participants in the case.
"To avoid prejudice to its criminal investigation and any directly related criminal prosecution, the Government seeks a stay of discovery in this action until its criminal investigation and any directly related criminal proceedings are resolved," the motion said.
The motion says the Coast Guard notified the U.S. Attorney's Office of its preliminary probable cause determination on August 13.
That inquiry determined the deaths "resulted from the misconduct, negligence, or inattention to the duties of the captain of the vessel at the time of the sinking, which is a violation of federal criminal law," according to the court document.
The U.S. attorney's investigation is in its early stages and "several agents/employees/officers of Ripley already have been notified that they are subjects and/or targets," the motion says.
A statement late Wednesday from Ripley declined to comment on the motion because of the ongoing investigation, but said, "We continue to fully cooperate with federal and state authorities, including the NTSB. We are providing all documentation and materials requested in the case and are complying with all hearing procedures."
The court document also indicates investigators want to talk to the captain of another duck boat that made it back to shore as a storm roiled the water of Table Rock Lake near Branson and swamped the other craft. That duck boat captain may have broken federal law, the Coast Guard said, by negligently operating the vessel and putting people's lives at risk, the document says.
CNN reached out to both captains on Wednesday but didn't get an immediate reply from either.
Video showed storm swamp boat
The first 911 call for the duck boat sinking came at 7:09 p.m.
According to weather data, a severe thunderstorm traveled hundreds of miles, prompting severe-weather alerts as it moved along, before it hit the lake.
Counties to the northwest of the Branson area were issued thunderstorm warnings at 5:45 p.m. The Branson area was placed under a severe thunderstorm warning shortly after 6:30 p.m.
A woman who was on the nearby Showboat Branson Belle, a riverboat docked near the sinking ship, recorded video of the duck boat sinking.
Her video shows at least three vessels on the lake, including the two Ride the Ducks boats rocking and tilting to the side as ripples turned into massive waves.
Strong winds whipped waves head-on onto the boats.
Duck boats' long history
Duck boats are amphibious vessels that travel on both land and water, and are popular among tourists in major cities. The boats' history dates to World War II, when such vessels were used because of their versatility.
In Branson, they are driven along city streets for part of the tour before the driver hands off to a captain who uses a ramp to enter the lake.
The driver of the duck boat was killed in the sinking. Fourteen people survived.
Branson, a popular family vacation destination, is about 200 miles southeast of Kansas City, Missouri.