The operator of a boat involved in a fatal July 4th incident on a northern Minnesota lake began drinking rum and Cokes that day starting around 9 a.m., according to a criminal complaint filed Tuesday.

A 50-year-old woman from Eden Prairie apparently drowned after she was pitched from the boat when it hit a wave at high speed, the complaint said.

Matthew A. Kinghorn, of Minnetonka, was charged in Beltrami County District Court with criminal vehicular homicide. He has been jailed since soon after the accident occurred about 4:15 p.m. on Cass Lake.

Killed was Brenda L. Larson, 50, of Eden Prairie, a swim coach for a club in her hometown. Kinghorn and his 3-year-old son were also tossed from the boat but were quickly pulled from the lake by passing fishermen. A fourth person, Kinghorn's 43-year-old wife, Jennifer, managed to remain in the boat.

The complaint against Kinghorn said Larson's death "was consistent with drowning." Only the child was wearing a life jacket, according to Sheriff Phil Hodapp.

A preliminary breath test administered to Kinghorn by a sheriff's deputy recorded a blood alcohol content of 0.125 percent nearly 90 minutes after the incident, the complaint noted. That level is well above the legal limit of 0.08 percent for driving a motor vehicle or a boat in Minnesota.

According to the complaint, Kinghorn gave the following account to a deputy at the jail:

Kinghorn, his wife, his son and Larson set off in his 17-foot boat about 9 a.m. to the south side of Star Island. He said he had a rum and Coke while on the way.

From there, he headed to Cedar Island and drank a second rum and Coke. He had a third rum and Coke before leaving the island.

Kinghorn said he "got his boat into a plane" at 25 miles per hour and hit a wave on his way down, the complaint read. The impact jolted the boat and tossed him, his son and Larson into the water.

After passersby pulled Kinghorn and the boy out of the water, Kinghorn got Larson into his boat. He headed to Sail Star Marina as CPR was performed on Larson.

Only the 3-year-old among those onboard had on a life jacket, Hodapp said. Minnesota law requires flotation devices to be worn by anyone under age 10. Otherwise, boats must have a life jacket for each person aboard, which this craft did, the sheriff said.

Also legally required for boats 16 feet or longer is a lifesaving device designed for throwing, which this vessel also had, Hodapp said.

Even though the adults on board were not legally required to have on a life jacket, state Department of Natural Resources guidelines say "we highly recommend everyone onboard wears a life jacket at all times."

Larson was a swim coach for Team Foxjet in Eden Prairie, leading the club's youngest swimmers for the past six years.