Seven minutes after Sarah Anne Wierstad boarded a bus in downtown St. Paul Sunday night, she stepped off at the Beaumont and Burr stop, a block from her apartment on the city's East Side.

Moments later, she lay dead on the sidewalk, shot through the heart.

Details of her killing were spelled out in a Ramsey County criminal complaint filed Thursday alleging that Alvin Rudolph Bell, 24, fired four rounds, hitting the young mother twice. The second-degree murder charge, which did not identify a motive, said investigators found Bell's fingerprints on the kitchen window of her apartment.

Wierstad's mother and a close friend said Thursday that they were convinced Wierstad interrupted a burglary before being fatally shot. She and Bell, of St. Paul, had "no known prior connection," said Dennis Gerhardstein a spokesman for the Ramsey County attorney's office.

According to the complaint:

A witness heard shots, saw "fire coming out of the gun," and hurried to help Wierstad as she lay dying. The witness "used a blanket provided by neighbors to apply pressure" to Wierstad's chest wound until police arrived.

The complaint continued:

Bell jumped into a car that sped away and later used Wierstad's credit card to buy gas in south Minneapolis. Police found his fingerprints on a window where the screen was cut and evidence that someone had been inside her apartment on Bedford Street. Police also found a "set of keys that seemed out of place," dropped on the floor near the front door.

Wierstad's purse and cellphone were missing as well.

'A hardworking parent'

As a single mother, Wierstad, 24, was determined to make her own way.

She moved to the Railroad Island neighborhood in July with her 5-year-old daughter over her mother's objections. It wasn't safe there, said Julie Zietlow, who was making arrangements Thursday for her daughter's funeral.

"She wanted to be able to provide for her daughter. She wanted to do it as a hardworking parent," Zietlow said.

One of Sarah's close friends, Jess Cimbura, described her as someone "who never got a break" because of the long hours she worked.

"Everybody loved her," Cimbura said. "She had a lot of ambition. She wanted to get her daughter out of the neighborhood. She wasn't OK with getting by, she wanted to be somebody."

The narrative of what happened in the minutes before Wierstad was shot less than a block from the bus stop wasn't explained in the criminal complaint. But a security camera recorded Bell's vehicle parking across the street from Wierstad's apartment at 7:35 p.m., about 17 minutes before the shooting and 11 minutes before she arrived on the bus.

Soon after Bell had parked, Wierstad boarded a bus for the ride home after ending her 12-hour shift as a cook at the Alton Memory Care assisted living center in St. Paul, where she worked for A'viands food services management company. She also had worked in the kitchen of the Ramsey County jail and was studying at Le Cordon Bleu to become a chef.

That night, her daughter's paternal grandmother was caring for the girl.

Investigators working the crime scene later found one shell casing from a 9-millimeter handgun on the sidewalk and three more in the grass. One round struck Wierstad in the left foot. An autopsy determined that she died from a second shot that tore through her arm and heart, according to the criminal complaint.

Witnesses and neighbors tried to save Wierstad before emergency help arrived, but she was pronounced dead at Regions Hospital.

After the shooting, officers entered Wierstad's apartment out of concern for Wierstad's daughter and "to make sure there were no other victims," the complaint said. No one was home, but closets were open in both bedrooms and purses that "appeared to have been thrown down" were found on the floor, the complaint said.

Zietlow said Thursday that she thought her daughter had interrupted a burglary, and Cimbura said neighbors told her they thought she was fleeing an assailant when she was shot in the foot. A few seconds of silence followed the first shot, followed by three more in quick succession.

All of Wierstand's money had gone to paying bills and to her daughter's care, said Cimbura, a former roommate. "She put her daughter before everybody in the world," and had recently taken her to Disney World, Cimbura added.

Bell's criminal history includes two "violent crime" convictions in Hennepin County, a two-year sentence for first-degree aggravated robbery in 2009 and a three-year sentence for attempted first-degree aggravated robbery with a firearm in 2010 when he was implicated in a foiled holdup of a convenience store in Excelsior. He has served time in St. Cloud, Stillwater, and Faribault prisons and on supervised release.

He is being held in the Ramsey County jail on $1 million bail.

Meanwhile, a 42-year-old woman arrested Tuesday by police in connection with the case was released from jail. Charges against her are not expected at this time pending further investigation, Gerhardstein said.

Wierstad's shooting death was the 10th homicide in St. Paul this year and the third on the East Side over the past week. In 2014, a total of 11 homicides were reported in the city.

Services for Wierstad will be held Friday at noon at Sandberg Funeral Home, 2593 E. 7th Av., St. Paul. Visitation begins at 11 a.m.