An adult woman was fatally stabbed at a Longmont apartment complex Saturday evening and police arrested a 15-year-old Lakewood boy seven hours later on suspicion of first-degree murder.

Longmont police responded to The Shores at McIntosh Lake at 6:12 p.m. Saturday and found a woman suffering from a stab wound. The suspect had fled the scene, police said.

The woman was taken to Longmont United Hospital, where she later died, according to police.

Police have not released the woman’s name, nor that of the suspect, who was taken into custody shortly after 1 a.m. Sunday in Lakewood.

Sgt. Matt Cage said police have not determined the exact circumstances that led to the stabbing, but he described the case as “tragic.”

“We are heartbroken for the family,” Cage said. “The police department is heartbroken at this.”

Police taped off an apartment inside the large, gated complex that sits at the corner of Colo. 66 and Airport Road on the northern edge of Longmont. Outside, investigators also could be seen stringing police tape around a black Hyundai Elantra and a grey Ford Five Hundred in the parking lot.

The woman’s death on Saturday marks the second homicide in Longmont in 2017. Joseph Keith Anderson, of Northglenn, fatally shot 33-year-old Keith Williams in the parking lot of Walmart in July, but he was not charged after the Weld County district attorney ruled the shooting to be self-defense.

Should the woman’s death be ruled a homicide, it would be the ninth in Boulder County this year.

John Bear 303-473-1355, bearj@dailycamera.com or twitter.com/johnbearwithme