The family of a grocery store owner killed earlier this year in a robbery at her store said Tuesday they are heartened by the arrests of three suspects but question whether they will ever understand why she was gunned down.

Lydia Alvarado, a 39-year-old mother of two, was fatally shot Jan. 26, after three men entered her store, the Azteca Grocery on Alpharetta Street, Roswell police say. The assailants left the grocery with two bank bags of money, police said.

In a news conference outside Roswell police headquarters, Alvarado's siblings and ex-husband said they are continuing to struggle with her slaying.

"We have to know why," said Maria Flores, her younger sister. "Why did they have to kill Lydia?"

When asked to describe her sister, Flores responded: "She was beautiful, inside and out. A great mother, a great sister, a great daughter."

Police say they have no evidence that the men charged in the killing knew Alvarado. Over two days this past week, police announced the arrests of three men. Each is charged with felony murder, aggravated assault and false imprisonment. Joel Augusto Boyce Douglas, 25, was arrested Sunday after a standoff with Fulton County's SWAT team.

Samuel Alfonso Boyce, 30, of Douglasville, was arrested on unrelated charges last month in Clayton County. Last Wednesday, police arrested David Alberto Luna, 31, in DeKalb County.

Alvarado, a graduate of Roswell High, was the fifth of six children in a Mexican-American family, and moved with her family from Chicago to the northern suburbs of Atlanta as a teen. She opened her store in Roswell 15 years ago, said her older brother, Arthur Macias. She had a reputation for being generous with patrons.

"If you would go to her grocery store, she would be the first to donate," Macias said. "She helped people who were needy. She even gave credit to people who were unable to pay for their food."

The family has since sold the store.

"I just wonder how something like this could happen to Lydia," said another brother, Raul Macias. "It's much more difficult to understand because of the kind of person she was."

Alvarado's two daughters, ages 11 and 13, are living with their father, Jesse Alvarado.

The girls are doing well with the support of family and friends, Alvarado said.

"There are things that nothing can fix," Alvarado said. "God forgives. Can I? I have to find it in my heart for us to be at peace."