DENVER, Oct. 23— The shooting stopped last April when the two Columbine High School students finally turned their guns on themselves.

But the devastation that left 12 other students and a teacher dead in Littleton, Colo., continues to claim victims, and when the mother of a student injured by the gunfire shot and killed herself on Friday, she simply became the latest.

Experts say that often the aftereffects of killings can endure for months, even years, as relatives and friends of the victims struggle to absorb their loss and define a new sense of normalcy.

''One of the things we often see after a mass tragedy is higher divorce rate, an increase in alcohol and drug use, and more car accidents, all because of the trauma people suffered,'' said Krista R. Flannigan, a victims services consultant in Idaho Springs, Colo., who works with many of the families of students who were killed or injured in the Columbine shootings.

Even before the mother, Carla June Hochhalter, 48, walked into a pawnshop in Englewood on Friday and asked to see a revolver, friends saw disturbing signs and wondered how deeply she had been affected by the shootings. Mrs. Hochhalter's daughter, Anne Marie, a Columbine senior, was shot in the back and the chest in the rampage on April 20. She is paralyzed from the waist down. As one of the most severely injured of 23 people who survived bullet wounds, she spent four months in the hospital.

Only this month, Anne Marie regained some movement in her legs, and, along with her parents and brother, Nathan, a student at Columbine, moved into a house that volunteers renovated to accommodate her wheelchair.

Of Mrs. Hochhalter, ''Six months of being heartbroken just got to her,'' Connie Michalik, the mother of another Columbine student who was shot, said today. Mrs. Michalik's son, Richard Castaldo, is confined to a wheelchair.

Mrs. Michalik became a close friend of Mrs. Hochhalter and her husband, Ted, an emergency management specialist with the United States Bureau of Reclamation, after the shootings. But she said she always found it easier to engage Mr. Hochhalter in conversation.

''The first day I met her, she was distraught,'' said Mrs. Michalik, who considers parents to be the second victims of the shootings. ''We were all basket cases.

''I didn't see her as any different from any of us, all upset mothers,'' she said. ''But she never got to a point past that, and moving was very traumatic for her. It was too much at once, and I think she was just worn out and couldn't take it anymore.''

Mrs. Hochhalter entered the pawnshop around the same time that Anne Marie and her father were visiting Leawood Elementary School, several blocks from Columbine, to thank students who had raised money for her rehabilitation.

The police said Mrs. Hochhalter asked to look at handguns and then pointed to a .38-caliber revolver in a glass case and said she wanted to buy it. As the clerk turned to begin the paperwork, the police said, Mrs. Hochhalter apparently loaded the gun with two bullets she had carried into the shop. She shot once into a wall and then pointed the gun at her head and pulled the trigger.

Mrs. Hochhalter's death came three days after a 17-year-old Columbine student was arrested after classmates reported to school officials that he had been threatening to ''finish the job'' started by the two shooters on April 20, Eric Harris and Dylan Klebold. The student, who was not identified by the authorities because of his age, was being held on a $500,000 bond.

In recent months, officials have grappled with other issues that reflect the enduring anguish of the shootings. The family of one victim, Isaiah Shoels, is suing the families of the shooters. More than a dozen families have notified the school district and Jefferson County that they intend to sue them over tactics used by the police on the day of the shootings.

And some families have even squabbled over how to memorialize the victims.

''It's been an extremely trying time,'' said Rick J. Kaufman, a spokesman for Jefferson County schools. ''It's important that we focus on getting back to normal again.''

But Ms. Flannigan, the consultant, said the concept of ''normal'' had forever changed for the families of the victims because of how the shootings have affected their lives.

''We need to prepare ourselves,'' she said. ''The trauma is not over. We will continue to see traumatic responses, and no one knows how long it will be until they end.''

Carla June Engelstad Hochhalter