by Leanne GreggNBC News
Colorado police have identified the gunman killed in one of two shootings targeting religious centers on Sunday.
The gunman has been identified as 24-year-old Matthew Murray of Englewood, Colorado.
The first attack happened early Sunday inside a training center for Christian missionaries in the Denver suburb of Arvada.
A man looking for a place to sleep walked into a dorm and shot four people after he was turned away.
26-year-old Tiffany Johnson and 24-year-old Philip Crouse died from gunshot wounds.
12 hours later came the second attack, this one at the New Life Church in Colorado Springs.
The gunman opened fire on a crowd of people coming out of a church service, shooting four parishioners.
Two have died, 18-year-old Stephanie Works and her 16-year-old sister Rachel.
Their father was also shot, and is in fair condition.
A volunteer church security guard shot and killed the gunman, and is credited with saving lives.
"Her role was to provide security and she did her job. She was a hero. There could have been a great loss of life yesterday. She probably saved over a hundred lives," said Senior Pastor Brady Boyd.
Church member Larry Bourbonnias had been shot and saw the security guard take down the gunman.
"I told her that's the bravest thing I've ever seen, and she said, 'I was just praying.'That was pretty powerful stuff. Very, very brave," he recalled.
As the two communities mourn, investigators are still trying to determine whether Murray is responsible for both shootings.