The grandmother of an Iowa man who drowned over the weekend at Lake of the Ozarks while under arrest says she was told that the life jacket an officer put on him was not properly secured.

The Missouri Highway Patrol told the St. Louis Post-Dispatch that Brandon Ellingson, 20, went overboard while being transported from the lake about 5:20 p.m. Saturday after being arrested on suspicion of boating while intoxicated.

The Highway Patrol said the circumstances of Brandon Ellingson’s drowning are under investigation. A patrol dive team using sonar recovered Ellingson’s body about 11:30 a.m. Sunday at a depth of about 80 feet near where he went in, officials said. The scene is near Gravois Arm, in Morgan County, about 140 miles southwest of St. Louis.

Ellingson was handcuffed behind his back, said Sgt. Paul Reinsch of the patrol. The trooper, Anthony C. Piercy, 42, was driving the 2008 Donzi patrol boat and had put Ellingson in a standard “Level 3” life jacket, which looks like a vest and has three front buckles. Piercy was driving Ellingson to a zone station to give him a breath test.

Ellingson was sitting next to Piercy when suddenly the prisoner stood up, took a few steps to the boat’s right side and went into the water. It is not clear how fast the boat was going or how the life jacket came off.

“He had it on when he entered the water but it came off at some point after he entered the water,” Reinsch said.

Reports say the officers made every attempt to rescue the man. One even jumped in the water and grabbed Ellingson but lost his grip and could not locate him again.