Angela Washington’s aunt in Missouri worried about her. The two had been like-minded and close growing up in Maryland. “Twins,” they had called each other.

Barbara Simms, 62, had once worked as a probation officer. Her niece became a private security guard — an armed special police officer, according to authorities — at an apartment complex in Southeast Washington that had experienced crime problems.

On Tuesday night, the 41-year-old Washington, a mother of four from Suitland, Md., was at work when she was fatally shot on a street outside the Oak Hill Apartments, a complex of nine buildings along the 3300 blocks of Wheeler Road and 10th Place SE in Congress Heights. Police said she was in her uniform and carried a firearm.

Simms said she had called her niece Tuesday morning to check up on her after learning of another relative’s illness.

“I told her, ‘Life is short, I don’t know how long we’ll be here,’ and that I loved her,” Simms said. Hours later, she learned Washington had been killed.

“We knew she had a dangerous job,” Simms said. “But she really loved what she did. She died a soldier. They really didn’t have to take her life like that.”

Police have not made an arrest and have not divulged details of what they believe happened, saying only they are looking for a white Toyota Camry with dark tinted windows. Authorities have not said what role that Camry might have had in the shooting, which occurred about 8:40 p.m.

“I want to find the person who murdered this young lady, just like I do for all families who experience a loss in a violent crime,” Police Chief Robert J. Contee III said Wednesday, urging people to step forward and help.

“When community and police work together,” he said, “I know we can bring this case to closure.”

Washington became the latest victim in a growing number of homicides that has now reached 154 in the District, a 12 percent increase from this time last year. It also came at the end of violent day in which at least nine people were shot and wounded, two of them children, with five of the victims struck in front of a convenience store.

A D.C. police spokesman said Washington had worked for Washington Field Protective Services, based in Oxon Hill, Md. A company representative did not return calls Wednesday.

Simms said Washington had recently returned to her job as a security guard after a hiatus, and had been promoted. She had four children, ages 16, 18, 19 and 21, and a 1-year-old grandson.

The aunt described Washington as “smiley and bubbly,” and said she “took pride in the way she looked.”

Other relatives said they were not up to talking at this moment.

Special police officers are security guards licensed by the District who have arrest powers limited to specific properties. They typically work for private security companies contracted by businesses, property owners and governments.

Contee confirmed that Washington was working at the Oak Hill Apartments when she was shot on a street off the property grounds.

A lawsuit that had been joined last year by the D.C. attorney general’s office alleged housing violations at the property and also said the neighborhood had experienced a steady stream of violent crime. The complex has since come under new ownership.

Representatives from the management company did not return calls and an email seeking comment. Efforts to reach Oak Hill’s owners were not successful.

Alice Crites contributed to this report.