The mother of a teen accused of shooting his younger brother to death was frustrated in her efforts to get the Department of Children and Families to take control of the older boy, relatives told the Herald, as Mayor Martin J. Walsh and lawmakers said the tragic case should become part of the ongoing investigation of the embattled child welfare agency.

“I never expected this to happen, but if he had been locked up and safe, none of this would have happened,” the woman’s niece and former high school classmate, said of Friday’s fatal shooting of her 9-year-old cousin, allegedly by his troubled 14-year-old brother in the family’s Morton Street 

“She’s a really, really good mom and she was trying so hard. She even went to them crying. They never did anything,” the mother’s sister claimed of DCF.

The 42-year-old mother, whose sister said she was at her day care center job when the youngest of her three children was killed, “wanted (the 14-year-old) to be in a place where they could take care of him because she didn’t want anything bad to happen to him. They said, ‘No, you have to take him back,’ ” the sister claimed.

The boy will be arraigned in Dorchester Juvenile Court today on charges of involuntary manslaughter, delinquency and unlawful possession of a firearm.

Police have said a 13-year-old in the home was arrested last year after becoming violent and threatening.

“She was afraid of him, afraid of his behavior,” the niece said, adding the suspected shooter “was driving her crazy” while the slain boy “was the light of her eyes.” The sister said the mother is so distraught, “She can’t even talk. She’s just crying, crying and crying.”