Teen, mother were slain after a grand jury date

It was unclear what, if anything, Sanchez told authorities about the June 5 shooting, which left another man injured. Although the officials told the Globe that Sanchez was brought to court in the hope he would testify, Jake Wark, spokesman for Suffolk District Attorney Daniel F. Conley, said that Sanchez was “not a cooperating witness’’ in Martinez’s homicide or any other slaying.

Diomedes Pimentel, who lost his daughter and grandson in the shooting, said a relative told him that the two went to court together but was unaware of what transpired there.

They died “savagely,’’ he said. “You never think something like this can happen.’’

The killing of Sanchez and his mother, Elvira Pimentel, 43, has renewed concerns about the risks of providing police with information about crimes, a longstanding problem in many Boston neighborhoods. It also underscores the struggle of witnesses who must decide whether to come forward when they live in neighborhoods where even the perception that one has cooperated with authorities can be deadly.

“People don’t understand that part of the reason why they’re uncooperative is because either themselves as individuals or their families are being threatened,’’ said the Rev. Jeffrey Brown, executive director of the Boston TenPoint Coalition, an antiviolence organization.

Sanchez’s upstairs neighbor, 17-year-old Laquan Miller, was arrested July 25 in the shooting of Martinez. Miller, who was a student at South Boston Education Complex, has pleaded not guilty.

Wark declined to comment on the grand jury.

“It’s an open investigation, and we’re not in a position to discuss potential motives,’’ Wark said. “Moreover, individuals who do cooperate with our investigations have a wealth of assistance available to them,’’ including a relocation program for witnesses, their families, and anyone else who might be in danger.

Boston police declined to comment on the case, saying that the killings of Sanchez and Pimentel remain under investigation.