LAFAYETTE - The man accused of killing a missing Lafayette man appeared in court for the first time on Tuesday.

Russell Britton, 58, will be formally charged on Thursday with first-degree murder, felony murder and narcotics-related charges.

Britton, as well as Moises Cazares Mendez, 26, are accused of killing 25-year-old Nate Tallman during or after an apparent "marijuana transaction."

According to Britton's arrest affidavit, Tallman died as a result of a drug transaction. Court documents say on Jan. 21, Tallman was on his way to meet Britton to "conduct a marijuana transaction." Family and friends told police they haven't heard from him since.

Britton is being held at the Boulder County Jail with no bond. Mendez is being held at the Las Colinas Detention Facility in San Diego, Calif. on a $1 million bond.

Mendez was arrested by U.S. Border Patrol on Saturday. The agency doesn't comment on individual arrests and declined to tell 9NEWS the circumstances of Mendez's arrest. His arrest affidavit is sealed.

Tallman was first reported missing on Jan. 23. According to the Britton's arrest affidavit, Tallman's phone records show he talked to Britton multiple times. Tallman's phone pinged off cell towers near Britton's Larimer County home.

Britton was interviewed multiple times by police and said he spoke to Tallman, but that Tallman never showed up at the arranged time.

On Feb. 13 around 11 a.m., a person found Tallman's vehicle and notified police. It was located near Foothills Highway and South Boulder Road in Boulder.

In Britton's van, police found blood in the rear of the car. The blood matched Tallman's DNA profile. Britton had previously told police Tallman had never been in his van.

On March 13, Tallman's body was discovered just north of Lusk, Wyo. The autopsy showed Tallman died from a gunshot wound.

Britton declined 9NEWS interview request.

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