Police now believe one person was inside a Kingdom Hall in Thornton when pipe bombs burst through a window Sunday. A shooting in the parking lot unfolded next — ultimately leaving a married couple dead in an apparent murder-suicide as unsuspecting congregation members started arriving for their Sunday morning meeting.

“Either the man, the woman, or both the husband and wife, the two deceased, threw three different incendiary devices through a window, breaking it,” Thornton Police Department spokesman Officer Joe Walker said on Monday.

Investigators declined to reveal the identification of either person killed, or speculate on any potential motive. The Adams County Coroner did not respond to requests Monday for identifications or autopsy results.

Police were still working to unravel details about the Christmas Day incident, but believe the husband shot and killed his wife in the parking lot before killing himself. The attack began shortly after 9 a.m. when one or both of the two killed threw the incendiary devices into the Kingdom Hall of Jehovah’s Witnesses on Milky Way. The hall conducts multiple regular meetings on Sundays, starting at 9:30 a.m.

Police initially received reports of a structure fire and later reports of a shooting. The lone person inside the hall at the time of the incident may be how the call to police about a structure fire initiated, although Walker said investigators are still sorting out who called police regarding a fire and who made reports about a shooting. Investigators interviewed witnesses into the night.

Neither the man nor the woman entered the building. None of the incendiary devices detonated. They were described by investigators as “pipe bomb in style,” Walker said, although that could include a wide range of explosive devices.

Only the man and woman were shot. Walker did not know what type of firearm was used in the shooting, nor how many shots were fired.

“No shots (were discovered) at the building or inside the building,” he said.

The coroner has not released the identity of the man and woman, and Walker said police are still looking into whether the couple was known to law enforcement before the Sunday incident. The couple were adults, but Walker did not release their approximate ages.

Investigators are also working to learn more about the couple’s past relationship with Kingdom Hall, where they were former congregation members.

“Hopefully we will know more on that soon,” he said.

Representatives of the Kingdom Hall could not be reached for comment. The Sherrelwood Congregation of Jehovah’s Witnesses released a statement on Sunday calling the incident an “unprovoked attack” that left the community shocked and saddened.

“Our hearts go out to the family and friends of those who have been traumatized by the heinous actions that took the life of an innocent victim and threatened the lives of many others,” the statement said. “We are praying for the families of all those affected.”

Neighbors awoke to gunshots and the sound of sirens as the shooting unfolded. At least two local residents saw a body in the parking lot as armed officers raced to the scene. Multiple agencies responded including the Adams County Sheriff’s Office, the Thornton Fire Department and the Adams County Sheriff’s Department’s Hazardous Materials Unit.

Josh Thorne, who lives in a nearby apartment, said shootings and police chases are common in the area but not at the hall, which he described as a quiet place. Another resident who did not want to be named watched police barricade the church where a man’s body lay in the parking lot.

“That was the first dead body I’ve seen,” the man said.

Reporter Kyla Pearce contributed to this story.