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Ex-husband of slain Mont. woman arrested in Ariz.

SHARE Ex-husband of slain Mont. woman arrested in Ariz.
This image provided by the Phoenix Police Department shows Walter Larson who was arrested Wednesday Feb. 22, 2012 in Arizona, suspected in the death of his ex-wife, whose body was found in the Yellowstone River in 2008. Larson was being held on $500,000 b

This image provided by the Phoenix Police Department shows Walter Larson who was arrested Wednesday Feb. 22, 2012 in Arizona, suspected in the death of his ex-wife, whose body was found in the Yellowstone River in 2008. Larson was being held on $500,000 bail pending extradition to Montana on charges of deliberate homicide and tampering with evidence.

Phoenix Police Department, Associated Press

HELENA, Mont. — Montana and Arizona authorities on Wednesday arrested a man suspected of strangling his ex-wife and then dumping her body in the Yellowstone River in 2008.

Walter "Marty" Larson was apprehended as he was leaving his Phoenix home for work, said John Doran, a spokesman for the Montana attorney general's office. He was being held on $500,000 bail pending extradition to Montana on charges of deliberate homicide and tampering with evidence.

Susan Casey, a 34-year-old mother of four who lived in the eastern Montana town of Glendive, was reported missing by her family on April 12, 2008. Her disappearance prompted a search of nearly 1,700 square miles that involved dozens of volunteers on horseback, foot and all-terrain vehicles.

A Montana Fish, Wildlife and Parks employee found her body the next month near the town of Fallon, about 30 miles upstream from Glendive. The Dawson County Coroner concluded that Casey was strangled and there was no evidence that she was alive when she entered the water.

Larson, now 40, was arrested two days after Casey's disappearance for violating a restraining order she had filed against him in 1998. A judge dismissed the charge because Larson hadn't been notified of the restraining order.

Casey had remarried, but she was separated from her husband and they were planning to get a divorce when she disappeared, according to charging documents.

The night before she was reported missing, her boyfriend, Brad Holzer, picked her up at about 11 p.m. They drove to the river and drank beer, and Holzer brought Casey back to her apartment at about 5 a.m., but he did not see her enter, the documents said.

One of Casey's children said that when she woke up that morning, her mother was not home and her bed had not been slept in.

Billings police interviewed Larson at his apartment there the evening Casey was reported missing. He told police that he and Casey had been planning to get back together after her divorce.

He said he was worried that she might have been drinking and driving the night before, so he drove to Glendive to try to find her, arriving after 4:30 a.m. He told officers that he knocked on her apartment door, but got no response, so he parked his vehicle around the corner.

He said that after waiting for some time, he concluded that she had been drinking and passed out, so he decided to leave.

But surveillance video from a nearby ATM machine confirmed that a vehicle that looked like Larson's was at Casey's apartment before and after Holzer dropped her off, and footprints were discovered in a recess near the front door.

The day before her disappearance, Casey had complained that Larson had been calling her and her husband and asked her daughter how to block numbers on her cellphone.

Court records said a search of his cellphone showed he made 44 calls to Casey between April 10 and April 12, 2008.

Holzer had received emails the day before from a person using the name Denise Johnson that asked "How's your girlfriend? How does your wife feel about it?" An investigation of Larson's computer showed Larson had created the email account.

Holzer's wife, Sam Holzer, said she received a call the week before from a person who said to tell her husband to "stop messing around with married women."

Larson also called Casey's father at 2 a.m. the morning she disappeared, saying he was worried about her because she had not called him back.

It was not clear in the charging documents why authorities waited nearly four years to re-arrest Larson.

"These cases take time and the state wanted to make sure it got everything exactly right on this one," Doran said.

He had been living in Phoenix and was working in nearby Scottsdale, Phoenix police said.

It was not clear when he moved to Arizona, Doran said.

Larson had not been scheduled for an initial court appearance by Wednesday afternoon and there was no immediate word on whether he will fight extradition.

Associated Press writer Mark Carlson contributed to this report from Phoenix.