A gunman opened fire in a training center dormitory for young Christian missionaries early Sunday after being told he couldn't spend the night, killing two of the center's staff members and wounding two others.
No arrests had been made by afternoon.
The shooting happened at about 12:30 a.m. at the Youth With a Mission center in this Denver suburb, police spokeswoman Susan Medina said.
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A man and a woman were killed and two men were wounded, Medina said. All four were staff members, said Paul Filidis, a Colorado Springs-based spokesman with Youth With a Mission.
The gunman came to the door of the dormitory seeking shelter, asking if he could spend the night, said Peter Warren, director of Youth With a Mission Denver.
When told he couldn't stay, the man walked inside, opened fire, then left on foot, Warren said.
Warren said he didn't know if any of the students or staff knew the gunman. He said the man had not been at a Christmas party that staff and students held at the dormitory that evening.
"We don't know why" he came to the dormitory, Warren said.
Witnesses told police that the gunman was a 20-year-old white male, wearing a dark jacket and skull cap, who left on foot. He may have glasses or a beard.
Police with dogs searched the area through the night, and residents of nearby homes were notified by reverse 911 to be on the lookout. Medina said residents were asked to look out their windows for any tracks left in the snow during the night. About 4 inches of snow had fallen in the area in the past day.
Brady White, who attends Faith Bible Chapel, where the center is located, said students he spoke to called the experience "terrifying."
"They're just wonderful people," White said of the center's students. "Their mission is to know God and to make him known."
Police identified the victims as Tiffany Johnson, 26, and Philip Crouse, 23. Youth With a Mission said Johnson was from Minnesota and Crouse was from Alaska. Their hometowns weren't immediately available.
About 45 people were evacuated from the dormitory and moved to an undisclosed location.
Cheril Morrison, wife of chapel pastor George Morrison, said Crouse had just hung up Christmas lights at her home and Johnson was "an amazingly beautiful person."
One of the injured men was hospitalized in critical condition and the other was in stable condition, police said. Both are in their 20s.
Mimi Martin, who lives near the center, said she received the warning call at about 9 a.m. warning neighbors to keep their doors and windows locked.
"Why would anybody want to hurt those kids?" Martin said. "I just pray for their families."
People bundled up against freezing cold attended Sunday services at the sanctuary, about 300 yards from the dormitory on the campus of the Faith Bible Chapel. Police kept tight security on the chapel grounds.
"We never doubted that we would have a service," said Cheril Morrison. "We felt like our church faithful all needed to be together."
Darv Smith, director of a Youth With a Mission center in Boulder, said people ranging from their late teens to their 70s undergo a 12-week course that prepares them to be missionaries. He said the center trains about 300 people a year.
Filidis said staffers are usually former missionaries themselves and that the "mercy ministries" performed by trainees include orphanage work. He said he didn't know where the group being trained in Arvada was going to be sent.
Youth With a Mission was started in 1960 and now has 1,100 locations with 16,000 full-time staff, Smith said. The Arvada center was founded in 1984.