One of two brothers believed to have murdered a missing Washington state couple turned himself in to U.S. Marshals at the U.S.-Mexico border, authorities said Monday night. 

The Snohomish County Sheriff's Office confirmed to Q13 Fox that Tony Reed, 49, was booked into the San Diego County Jail in California. Further details of Reed's arrest were not immediately available. 

Reed is suspected of helping his brother, 53-year-old John Reed, murder Patrick Shunn and his wife, Monique Patenaude, of Arlington, Wash., last month. The couple have been missing since April 11 and their whereabouts remain unknown.

"We're definitely glad to have one [brother] in custody," sheriff's office spokeswoman Shari Ireton said. "We're hoping for more information about the bodies." 

The Reed brothers were charged with first-degree murder in the case April 19 after authorities said they had found "significant blood evidence" in the cargo area of the couple's cars that led them to believe they were killed. The brothers are believed to have fled to Mexico after the killings.

In court documents, the Snohomish County prosecutor’s office said the Land Rover and Jeep belonging to Shunn and Patenaude “had obvious blood pooling and smearing, and some blood splatter in their respective interiors." The vehicles were found down an embankment in a remote, wooded area near Oso, Wash. and authorities said surveillance video linked the Reed brothers to the vehicles' disposal.

Authorities say it is unclear exactly how the couple died, but the documents said a “fresh” 9mm shell casing was found just outside the locked gate that leads between the former home of John Reed and the Shunn/Patenaude home.

Authorities said John Reed had previously lived near the couple and had property disputes with them.

John Reed is still on the run and Snohomish Conty officials are soliciting tips from the public regarding his whereabouts. 

John Reed's car was found previously in central Washington, and detectives said the brothers had taken their parents' red Volkswagen.

John Reed tried to cash a check for $96,000 on April 14 before he went on the run from police, according to court documents. The brothers had not been identified as suspects at the time. Ireton has said the bank wasn't able to cash the large check but issued five smaller cashier's checks to John Reed. One check had been cashed before authorities put a hold on them.

Authorities had said the brothers could have been heading for Mexico. Detectives found a car in Phoenix that had been driven by the Reeds and said the suspects took another car with an Arizona plate.

A license plate reader captured that plate near Calexico, Calif. and the Reeds themselves had been spotted in the country several times, authorities said.

Tony Reed has dozens of arrests and twice was under state supervision -- from 1989 to 1991 on drug charges, and from 1994 to 2003 for three misdemeanors, one count of attempting to elude police and one count of third-degree assault.

John Reed has been cited for mostly minor offenses, including driving without a license and collecting wood without a permit. He served five years under supervision of the Department of Corrections in the late 1990s for attempting to elude police in Whatcom County.

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