ENGLEWOOD, Colo. -- Police have arrested a suspect believed to be responsible for a shooting just outside a Super K-Mart that killed one woman and critically injured another Sunday night.

Anthony Law, 39, was found at a nearby apartment early Monday, at about 12:40 a.m., and taken into custody.

The shooting occurred hours earlier by the entrance of the 24-hour K-Mart Super Center at Belleview Avenue and Broadway. Witnesses say it was about 7:50 p.m. when shots rang out just in front of the store.

Police say 43-year-old Kathy DeBell had just gotten off work and was waiting for a ride home when a gunman walked up and opened fire. DeBell, of Littleton, was shot in the chest and died of her injuries a short time later.

Claudia Nunez was a customer who was shopping with her young son when she was hit with gunfire just inside the store. She was shot in the lower back.

"That was a total shock to me. The lady had a 10-year-old boy with her. They took off running, crying 'Mommy,' and hid behind the service desk. Everybody was in shock, really scared, because we didn't know whether (the suspects) continued and ran inside the store or if they came back in," said witness Kelvin Dison.

Nunez, 30, is in critical condition at Swedish Medical Center.

A man shopping inside the store said that he heard five shots and thought they were fireworks.

"It sounded like Black Cats. It's the Fourth of July, the first thing that popped into my head was Black Cats (fireworks). I didn't think nothing about no guns ... I thought somebody was trying to play a joke and then I saw her fall and I went over and tried to help her out. So, some scary stuff," witness Victor Leija told 7NEWS.

The gunman then ran to a nearby apartment complex. Police and SWAT teams fanned out in the Englewood and Littleton neighborhood, looking for the gunman. Law was found inside an apartment at 201 W. Belleview.

Investigators did not say what prompted the shooting or what Law's possible motive may be. It doesn't appear that he knew either woman, police said.

Law was described as a "regular customer" who lives in the apartment complex across the street.

Friends say DeBell had spent part of the day Sunday joking with a friend about some of her store's more difficult customers. She had started working at the store just two weeks earlier, after deciding her commute to a Safeway store in Boulder was too far.

Debbie Gomnes was on her way to pick up DeBell when a store employee told her about the shooting on her cell phone. Gomnes later called DeBell's mother to give her the news. DeBell's mother, Annabelle Knapp, was in Omaha dealing with the recent death of her brother when she learned her daughter had been killed.