The gunshots were so loud that Jeanne Assam thought the shooter was already in the building.

A former police officer, Assam, 42, was on security duty Sunday morning at New Life Church here. Hours earlier, a 24-year-old who had been rejected from a missionary school in a Denver suburb had shot and killed two staffers there. Now he was spraying New Life’s parking lot with gunfire and pushing through the doors to the sanctuary.

Assam hid and inched toward the gunman, Matthew Murray, as dozens of terrified worshipers fled. She waited until he got close enough, revealed herself, aimed her pistol and fired. Murray dropped to the ground. He was carrying an assault rifle, two pistols and a backpack holding more than 1,000 rounds of ammunition.

“I just prayed to the Holy Spirit to guide me,” Assam said at a packed news conference Monday. “I give the credit to God. This has got to be God, because of the firepower he had versus what I have.”

Authorities on Monday said Assam saved untold lives as they described how Murray, the home-schooled son of a prominent neurologist, terrorized two religious facilities during a harrowing 12-hour rampage.

Police said it was unclear whether Assam’s shots killed Murray or whether the gunman, after being wounded, took his own life.

Murray killed two teenage sisters at New Life Church on Sunday afternoon and wounded their father and two other worshipers. The gunman had been at large since 12:30 a.m., when he attacked the Youth With a Mission school in Arvada.

Phil Abeyta, a pastor who is Murray’s uncle, spoke to reporters outside the school Monday afternoon.

“Our family can’t express the magnitude of our grief for the victims and families,” Abeyta said tearfully. “On behalf of our family, we ask for forgiveness. We can’t understand why this has happened.”

At Abeyta’s side was Peter Warren, the school’s director. Warren said that when Murray came to the school early Sunday asking to stay the night, staff members did not recognize him.After Murray was identified by police, the school realized he had attended its training program in 2002. The Arvada school is a branch of an international missionary program that trains thousands annually.

Warren said school officials refused to assign Murray to a mission because of an unspecified health problem that could make such work unsafe. Warren would not elaborate, and he and Abeyta left without taking questions.

Police said it appeared Murray acted alone, although they were still investigating whether he had help getting from Arvada to Colorado Springs.

In court papers, police said Murray had written threatening letters to the school and spent many hours a day on the Internet as a computer student, the Gazette of Colorado Springs reported.

He lived at home with his 21-year-old brother and his parents in a two-story brick home in an affluent neighborhood in Englewood, a suburb at the southern end of Denver’s sprawl. His father, Ronald Murray, is a neurologist who specializes in treating multiple sclerosis patients.

Colorado Springs Police Sgt. Jeff Jensen said it was too early to know what precisely motivated Matthew Murray. “This tragedy is just a little over 24 hours old and we’re still in the process of gathering information,” he said at an afternoon news conference.

It also was unclear why Murray traveled the roughly 75 miles from the missionary school in Arvada to New Life Church, which has a Youth With a Mission branch office. New Life achieved notoriety last year when its founder, Ted Haggard, was accused by a former gay prostitute of trading drugs and sex.

Murray apparently left smoke grenades as distractions at the western and southeastern entrances to New Life. Then he moved to the eastern parking lot and opened fire, hitting the Works family of Denver.

Stephanie Works, 18, died at the scene; her sister Rachel, 16, died in a hospital hours later. Their father, David, 51, was wounded in the groin and abdomen and was in fair condition.

Jensen said it was unknown whether Murray targeted the Works girls, who had reportedly gone on a Youth With a Mission trip overseas and frequented the group’s Arvada branch.

Early Sunday morning, New Life’s security director had warned Senior Pastor Brady Boyd about the missionary school attacks and recommended bolstering the church campus’ volunteer contingent of guards. At her home, Assam read online about the shooting and felt a chill.

A worshiper at the church, she also protects fellow parishioners and Boyd. She was working her regular shift Sunday afternoon. There were about 7,000 people on campus as the midday service wound to a close around 1:10 p.m. and Murray opened fire.

“I heard shots fired. There was chaos, there were a lot of people in the church,” Assam said. “The shots were so loud I thought he was inside. . . . It seemed like the halls cleared out; I saw him coming through the doors.”

Assam said she hid until he came close. “I came out of cover, identified myself and took him down,” she said. “I just knew I was not going to wait for him to do any more damage.”

She said she prayed before opening fire. “My hand wasn’t even shaking,” she said. “It seemed like it was me, the gunman and God.”

Wiry, with wavy blond hair and a dazed expression that came from not sleeping for 24 hours, Assam would not identify the law enforcement agency she used to work for, though she said she “loved being a police officer.”

The Rev. Boyd, who introduced Assam, stressed that all church guards were volunteers who worshiped at the church and were legally allowed to carry guns.

“Given the events of the past 24 hours, you understand why there is a need to provide security to the people who worship there,” Boyd said.

nicholas.riccardi@latimes.com

Riccardi reported from Colorado Springs and Correll from Arvada.