A grand jury has been impanelled to consider evidence in the fatal police shooting of Akai Gurley, the Brooklyn district attorney has announced.

Gurley, who was 28, was shot dead by a rookie officer on 20 November at the Pink Houses public housing block in East New York, in what police have described as an accidental discharge. Gurley, who was descending a stairwell in the block, was unarmed. He was described by NYPD police commissioner Bill Bratton as a “total innocent”.

“I pledge to conduct a full and fair investigation and to give the grand jury all of the information necessary to do its job,” Brooklyn district attorney Ken Thompson said in a statement announcing the grand jury, which will have the power to press criminal charges.

Thompson said there was no date at present for the grand jury to convene. He rejected calls for a special prosecutor to handle the case in the wake of perceived bias in recent grand jury decisions in the cases of Eric Garner and Michael Brown.

“I was elected by the people of Brooklyn to do this job without fear or favour, and that is exactly what I intend to do,” Thompson said.

The announcement came as it was revealed by the New York Daily News that an officer involved in the shooting texted his union representative instead of calling for medical assistance in the immediate aftermath of the shooting.

As rookie officer Peter Liang and his partner entered a darkened stairwell, Liang’s gun discharged and a bullet struck Gurley, who was with his girlfriend on the seventh floor, in the torso.

Quoting a number of unnamed law enforcement sources, the Daily News said that after the incident, neither Liang nor his partner, Shaun Landau, could be reached by their superiors for more than six minutes. The New York police department (NYPD) reportedly learned of the incident from a neighbour’s 911 call, after which it attempted and failed to reach Liang and Landau.

Kenneth Montgomery, the lawyer representing Gurley’s parents, told the Guardian the allegations, “if in fact true, [are] egregious on several fronts”. He said a grand jury could view such actions “as criminally negligent or an act of depravity”, revealing “a lack of humanity” on the part of Liang.

An NYPD spokesperson refused to comment on the case.

Gurley’s case is one of several in recent months in which the killing of an unarmed black man by police has provoked outrage and calls for change and accountability in law enforcement. On Wednesday, a Staten Island grand jury chose not to indict NYPD officer Daniel Pantaleo for using a chokehold in an arrest that caused the death of a 43-year-old man, Eric Garner.

Also on Wednesday, it emerged that a Cleveland police officer who shot and killed Tamir Rice, a 12-year-old boy carrying a fake gun, had previously been deemed unfit for duty.

Facebook Twitter Pinterest The Louis Pink Houses. Photograph: Lucas Jackson/Reuters

A law enforcement source told the Daily News the officers’ decision not to radio for help was mystifying: “The guy is dying and you still haven’t called it in?” The source said Liang and Landau eventually reported an accidental discharge.

Other sources said officers at the housing development had been explicitly ordered not to patrol the stairwells, a tactic known as “verticals”. After Gurley was shot in the chest, he and his girlfriend hobbled to find help two floors below. Gurley was pronounced dead at Brookdale Hospital later that night.

Hours before the grand jury announcement, Gurley’s mother, Sylvia Palmer, made her first appearance since her son’s death.

“I need justice for my son. I want my son to rest in peace with the respect he deserved,” Palmer said. “It’s like I feel like I’m lying in the morgue with him right now. I need my son back.”