DENVER (Reuters) - A 24-year-old man was formally charged on Thursday with murder in the fatal shooting of three people found slain last month in a Colorado mountain home filled with marijuana plants being grown inside the dwelling, prosecutors said.

Garrett Coughlin, charged with multiple counts of first-degree murder, is shown in this booking photo in Boulder County, Colorado, U.S. on May 16, 2017. Courtesy Boulder County Sheriff's Office/Handout via REUTERS

Garrett Coughlin appeared in Boulder County District Court to face three counts each of first-degree murder and felony murder, as well as aggravated robbery, presented in a criminal complaint, though he has yet to enter a plea in the case.

He is accused of killing Emory Fraker, 39, Wallace White, 54, and White’s 56-year-old wife, Kelly Sloat-White, a spokeswoman for District Attorney Stan Garnett told Reuters.

Their bodies were found on April 15 inside a house in Coal Creek Canyon, about 30 miles northwest of Denver, by police who paid a visit to the home to check on them when someone reported not hearing from the Whites for several days.

All three died from gunshot wounds. Investigators found more than 100 marijuana plants in the house and learned that cash in large amounts was typically kept there, according to an arrest warrant affidavit filed by the Boulder County Sheriff’s Office.

Police said the house was essentially being used as “an illegal grow operation” for cannabis. While pot cultivation for private use is allowed in limited quantities in Colorado, large-scale production requires a state license.

Coughlin, a resident of suburban Denver, is represented by the Public Defender’s Office, which declined comment.

Police said he became a suspect after he surfaced as an acquaintance of the Whites, and he was reported to be engaging in activities that seemed out of character.

“Two days after the homicide, witnesses saw Garrett with large quantities of marijuana packaged consistent with the victims’ and cash, which was unusual for Garrett,” the affidavit said.

The state crime lab also matched a slug removed from one of the victims to a handgun linked to Coughlin, the report said.

Police said Coughlin “never denied involvement” in the killings during questioning by detectives earlier this week. When confronted with the ballistics evidence, he asked for a lawyer, the interview ended and he was arrested, according to the affidavit.

Police Commander Mike Wagner said the investigation was ongoing and that further arrests were possible.

Coughlin, who remains held without bond, is due back in court on Sept. 7. If convicted of first-degree murder, he faces a mandatory prison sentence of life without parole.