(CNN) -- The gunman who killed two others before police ended his life in a shootout near Texas A&M University had been battling mental health issues on and off for years, his mother said.
Police say Thomas Caffall, known to his family as "Tres," killed a constable and a bystander and injured four others Monday before police fatally shot him.
His mother, Linda Weaver, said the family became worried after Caffall quit his job in January and announced that he would never work again.
"We had been very concerned about him," Weaver told CNN.
Caffall had withdrawn from the family, and the fear was that he might attempt suicide, his mother said.
But she never imagined that her son would hurt anyone else, or that his end would come so violently.
"Losing a child is a parent's worst nightmare. This is worse," she said.
Police said Caffall, 35, shot and killed Brian Bachmann, a constable for Brazos County, and Chris Northcliffe, an area resident.
Bachmann had approached Caffall's apartment to deliver an eviction notice, and Northcliffe just happened to be nearby.
Also nearby was Rigo Cisneros, a former Army medic who assisted both Bachmann and Caffall after the shooting.
As he lay dying, the gunman offered an apology for what he had done, Cisneros told CNN's Brooke Baldwin.
"He did ask me to apologize to the officer he had shot," he said.
Three College Station police officers and a woman were injured in the shooting, police said. The woman, Barbara Holdsworth, was in serious condition after undergoing surgery.
Investigators on Tuesday continued to process the crime scene.
The area covers "a couple of blocks," College Station Police Chief Jeff Capps said.
The suspect "fired multiple rounds and investigators have recovered long guns and a pistol from the scene," he said.
As the incident unfolded Monday, an alert warning of a gunman was sent out by Texas A&M, one of the state's flagship universities and a sprawling campus of nearly 47,000 students.
According to his Facebook campaign page, Bachmann was a 41-year-old from College Station who had been a Brazos County sheriff's deputy since 1993. The county's website indicated that his four-year term as constable -- an elected position that involves, among other duties, serving court documents such as eviction notices and subpoenas to citizens -- was set to expire on December 31, 2014.
Bachmann was an up-and-coming law enforcement leader who some expected to run for sheriff one day, said Marc Hamlin, the district clerk for Brazos County and friend of the slain constable for more than 20 years.
"He was a true public servant," Hamlin told CNN.
Whenever a group wanted a law enforcement officer or squad car for a community event, Bachmann was always the first to volunteer, Hamlin said.
He also volunteered to help his friends.
On Monday, Bachmann had lunch with his chief deputy, who had to deliver the eviction notice at the nearby residence afterward. Bachmann took the notice and volunteered to serve it himself, Hamlin said.
A search of court records showed no record of Caffall having run-ins with the law except for a traffic violation.
Caffall's mother described her son as an intelligent youth who wasted opportunities available to him.
"It's so hard to imagine that the really sweet kid you raised turned into a huge monster, and that is what he is now," Weaver said.
He enjoyed collecting weapons and refinishing them, Weaver said, so his owning guns wasn't worrisome, his mother said.
Weaver said Caffall had been very affected by the death of his father when he was 12. She said it is hard to comprehend how the same person would deprive Bachmann's children of their father.
Bachmann's three children -- ages 19, 10 and 8 -- would accompany their father on mission trips in Texas. On a recent trip, they built wheelchair ramps and roofs, Hamlin said.
"He was strong in his faith and strong in his family," he said.
Less is known about Caffall. He was divorced, and was in the constant companionship of a large Sheltie-mix named Lucy, his mother said. Lucy's fate is unclear.