About 120 people demonstrated in front of the State House in Boston Wednesday night to demand that cases of police killings in Massachusetts be reopened, and that prosecution of police involved in those killings be considered.

The event was organized by Mass Action Against Police Brutality, a local activist group. Several families and friends of people killed by police spoke to a mostly young and racially diverse crowd. Among them was Hope Coleman, the mother of Terrence Coleman, a Black man who was shot and killed by Boston Police in the South End four years ago. He was 31.

Coleman told of how she called 911 for emergency medical services for her son, who was suffering from mental illness and had stopped taking his medication. She said police showed up and took over the call, and shot her son dead when he wouldn’t cooperate with them.

“You come and kill my son when I called for the ambulance,” Coleman said through tears. “If I‘d known they were going to do that, I would have never called 911. I was doing what a parent is supposed to do. It didn’t help.”

Jennifer Root Bannon also addressed the crowd from the State House steps. Police say her brother Juston Root brandished a non-working gun replica in February at Brigham and Women’s Hospital before leading officers on a car chase. Root Bannon said police shot her unarmed brother 31 times, that he also had mental health issues, and that he was not a danger to anyone when he was killed. He was 41.

She told the demonstrators that police could not be trusted to investigate themselves.

“I call upon Marty, Mayor Walsh, Attorney General Maura Healey and Governor Baker,” Root Bannon said. “I ask you not to close your eyes and instead join us in making a concerted effort for lasting change. Governor Baker, I'm going to ask you again: Reopen my brother's case for an independent investigation, reveal the truth. My brother deserves it. My family deserves it. And the public deserves it.”

After the rally at the State House, the demonstrators marched to City Hall, with chanting lasting for an hour and a half. They chanted the names of many nationally known victims of police shootings, as well as people who have been killed in Massachusetts, followed by “Reopen the cases!” and “No justice, no peace; prosecute the police!”

The march ended after 8 p.m. in Peters Park in the South End, near where Terrence Coleman died. Organizers say they want to rename the park after Coleman.

Activists with Mass Action Against Police Brutality have started an online petition to demand that the Baker administration appoint a special prosecutor to investigate past killings by police.