DENVER (KDVR) — A woman is dead and a second is critically injured after a stabbing believed to be perpetrated by an 18-year-old suspect, who is also believed to be their family member.

The teen was arrested in connection with a deadly stabbing reported at an apartment in the 1300 block of Sweet River Circle on Sunday night, according to the Douglas County Sheriff’s Office.

Douglas County’s emergency dispatch was informed at about 11:36 p.m. of a possible stabbing in progress at the Madison Apartments at the Canyons. Based on the information given to dispatchers, deputies forced their way into the apartment, breaking through both an exterior door and an interior door.

Inside the apartment, deputies reportedly found one victim, a woman whose age was not provided, unconscious and not breathing with apparent stab wounds. They also found a second victim, a 20-year-old woman, with a serious arm injury that appeared to have been caused by a knife. She reportedly had stab and slash wounds all over her body.

Deputies began life-saving efforts, including applying a tourniquet to stop the bleeding. The sheriff’s office said that the second victim was transported to a hospital in critical condition but is expected to survive.

“Those deputies are actually credited with saving that woman’s life,” said Sheriff Darren Weekly in a press conference held outside the apartment on Monday afternoon.

Deputies said they used “rapid on-scene investigation” to identify and locate the suspect, 18-year-old Messiah Williams, who was naked in an open space south of the residence. He was reportedly taken into custody without incident.

He is facing charges of first-degree murder, attempted murder in the first degree with deliberation, assault in the first degree, and tampering with physical evidence. All of the charges are felonies.

Weekly said that he’s been in Douglas County for 32 years and could not recall the last time there was a homicide in Castle Pines.

“The only thing that I can say about our suspect and our victims is we do believe that they are all related — this was not a stranger assault,” said Weekly.

He said he believes all individuals involved were family members.

“It’s a very difficult case,” said Weekly. “We are talking to a lot of witnesses, both from part of the family as well as witnesses outside the family, to gather what led up to last night’s event happening, and to determine what exactly happened from there.

Weekly said the district attorney’s office has been working with the sheriff’s office since detectives arrived on scene, and said there have been no calls for service to the location previously.

He said there’s no danger to the public, and that the investigation is ongoing.