COLORADO SPRINGS, Colorado (CNN) -- The shooter at both religious institutions in Colorado on Sunday was Matthew Murray, a source familiar with what happened at both locations said Monday.
Two people were killed by a gunman early Sunday at Youth With a Mission in Arvada, Colorado, and two other died from gunfire outside a church in Colorado Springs about 12 hours later.
The Colorado Springs megachurch instituted security precautions after the shootings at the Denver area mission center, saving "hundreds of lives" at the New Life Church, senior Pastor Brady Boyd said Monday.
A New Life parishioner acting as a security guard shot and killed the gunman who entered the church Sunday afternoon after he had gotten no more than 50 feet inside the building, Boyd said.
Two teens, identified by police as Rachael Works, 16, and Stephanie Works, 18, were killed in what Boyd called "a senseless, random attack."
Boyd said the teens were sisters and were shot in the parking lot. Police said their father David Works, 51, was also shot and is hospitalized in fair condition with two gunshot wounds.
Boyd said the female security guard was a hero in preventing further bloodshed, rushing to confront the gunman just inside the church.
"She probably saved over a hundred lives," Boyd said of the guard, whom he said is not a law enforcement officer and used her personal weapon.
Boyd said the gunman, whom police have yet to identify, had no connection to the church.
"He simply showed up on our property yesterday with a gun, with the intention of hurting people, and he did," Boyd said.
The pastor also said New Life had taken extra precautions Sunday after hearing of the attack in Arvada, Colorado, early Sunday morning, in which a gunman killed two people after he was refused lodging at Youth With a Mission live-in Christian missionary center.
"Hundreds of lives were saved yesterday because of the plan that was put in place," said Boyd, who put the number of people on the church campus at the time as 7,000.
Authorities say the Arvada and Colorado Springs shootings may be related, and overnight police from Arvada executed a search warrant obtained by Colorado Springs police for an address in the Denver suburb of Englewood. Authorities did not say how the address may relate to the case.
Lt. Skip Arms of the Colorado Springs Police Department said that no motive has been determined for the gunman at the second shooting. The gunman's identity has not been released.
Police in the two cities say different weapons were used in the shootings -- a handgun in Arvada and a rifle in Colorado Springs. Watch police, heartbroken pastor react to attacks »
The first incident took place Sunday at about 12:30 a.m. at Youth With a Mission in Arvada. Police said a man with a beard, wearing a dark jacket, glasses, and skullcap, entered the facility, got into a dispute with a staff member about whether he could stay there for the night, and then opened fire.
Investigators tried to track the gunman through fresh snow with the help of dogs, but lost his trail in a heavily walked area, Deputy Chief Gary Creager of Arvada police said.
Then shortly after 1 p.m. in Colorado Springs -- about 80 miles south of Arvada -- a black-clad gunman opened fire on worshippers at New Life.
Youth With a Mission co-founder Peter Warren identified the two killed staff members as Tiffany Johnson, 26, and Philip Crouse, 24. He said they were cleaning up from a Saturday night Christmas banquet when the attack occurred.
Another staff member, 24-year-old Dan Griebenow, was in critical condition with a bullet in his neck as of Sunday night, and a second survivor, Charlie Blanch, was shot in the legs, the group said on its Web site.