By Rory Carroll

(Reuters) - Missouri has agreed to pay $9 million to the family of a man who drowned in 2014 when he was ejected from a boat while handcuffed and in a state trooper's custody, an attorney for the family said on Thursday.

Arizona State University sophomore Brandon Ellingson, 20, was vacationing with his family in Missouri when he was arrested by Highway Patrol Trooper Anthony Piercy for boating while intoxicated.

Ellingson, who was originally from Iowa, was leaving a restaurant-bar with seven friends en route to his parent's lake house on May 31 when he was taken into custody.

Piercy brought Ellingson onto his patrol boat, handcuffed him, and pulled a lifejacket over his head. But the lifejacket came off when Ellingson fell into Lake of the Ozarks, said Matt Boles, an attorney who represented the family.

Piercy attempted to rescue Ellingson after he fell overboard but was unsuccessful. Ellingson's body was retrieved the next morning.

A spokesperson for the state's Attorney General's Office, which represents state employees including state troopers in civil matters, declined to comment on the settlement.

Boles said Piercy was not properly trained and was traveling at speeds as high as 46 miles per hour with Ellingson in the boat. The settlement, which Boles said he expects to be finalized in the coming days, is the best outcome the family could expect.

"This family, Craig and Sherry Ellingson, have never really been about the money. But in civil litigation, especially wrongful death, you can't bring people back from the dead," he said. "The only way we can compensate those that are wronged is with the payment of money damages."

The Missouri State Highway Patrol have implemented a series of changes to its training regiment since Ellingson's death, Boles said. The patrol did not respond to a request for comment.

"This was about justice for Brandon and making sure no other family has to endure the pain and anguish of having to lose somebody at the hands of Tony Piercy," he said.

An investigation by the Kansas City Star determined that a 2011 merger between the Missouri Water Patrol and the Highway Patrol that was designed to save money and increase safety had left longtime highway troopers such as Piercy insufficiently trained to work state waterways.

The Ellingson family is now looking to the Missouri state court, where manslaughter charges are pending against Piercy, Boles said.

(Reporting by Rory Carroll in San Francisco; Editing by Alan Crosby)