The incident occurred at a home in unincorporated Weld County, outside Longmont, about 35 miles north of Denver, according to the Associated Press. One of the victims, 25-year-old Beatriz Cintora-Silva, was on the phone with 911 when she was shot and killed by her ex-boyfriend, Daniel Sanchez, 31.
Sanchez proceeded to pick up the phone and tell the 911 operator that he had killed three people and was about to kill himself; authorities say the dispatcher heard a single gunshot, and then silence.
The other victims were her sister, Maria Cintora-Silva, 22; and her sister's husband, Max Aguirre Ojeda.
According to Weld County Sheriff John Cook, Sanchez had been released on bail from a Boulder County jail on Monday, at 10 p.m., after having been arrested Saturday in Longmont.
Sanchez was charged with " domestic violence, kidnapping and false arrest for allegedly holding Maria Cintora-Silva against her will after their relationship ended."
Upon being released, Sanchez drove to the home where Cintora-Silva was staying with her sister and her sister's husband.
Sheriff Cook said that Sanchez gained entry into the house by force.
"He shot out the back door," Cook said. "He shot that out then gained entry into the house."
Several neighbors said they heard the gunshots as well as screaming coming from the house around 4 a.m. on Tuesday, as the events unfolded.
"It was just screaming. I couldn't hear what she was saying. It was just screaming," said Joyce Vibbert, adding that she was unable to see what was happening from a bedroom window.
Once investigators were on the scene, they discovered the bodies of Ojeda and his wife in one bedroom, and the bodies of Maria Cintora-Silva and Sanchez in another, as well as a .45-caliber Glock handgun near Sanchez's body, and 16 spent shell casings in various locations of the house, according to the AP.
A still-running pickup truck, with Texas license plates, was parked in the driveway.
Investigators said were able to search Sanchez's home, a house in the same neighborhood, and found the original box for the handgun used in the murder suicide, reports said. According to Sheriff Cook, the receipt was not found, and police were unable to determine when the gun was bought, according to several accounts of the incident.