Story highlights The case is drawing parallels to the shooting of Trayvon Martin

Kenneth Chamberlain accidentally set off a medical alert device, his family says

Police say they shot Chamberlain after he came at them with a knife

The family says video and audio recordings prove he was unarmed

It was just after 5 a.m. on a cold November morning in 2011 when Kenneth Chamberlain Sr., a 68-year-old former Marine with a severe heart condition, accidentally set off a medical alert pendant.

An ambulance was dispatched to Chamberlain's White Plains, New York, apartment, though police who respond to such calls as a matter of routine arrived ahead of the emergency medical workers.

Within the hour, Chamberlain, who is black, lay dying -- from two rounds fired into his upper body by a white police officer.

What led to the shooting of Chamberlain is the subject of a grand jury hearing underway this month, and a matter of heated debate between the White Plains Police Department and Chamberlain's family and friends.

Police say Chamberlain came at them with a butcher knife when they broke down the door after he refused to open it; the family claims the elderly Chamberlain was unarmed, and that he told police through the closed door that he did not need any assistance.

In wake of the case of Trayvon Martin, the unarmed, black 17-year-old who was shot and killed in Sanford, Florida, by a neighborhood watch volunteer, the Chamberlain case has gained national interest -- and national media attention.

More than 206,000 people have signed an online petition demanding "Justice for Kenneth Chamberlain Sr.," with many signatories drawing similarities between the case and that of Martin.

The petition, started by Chamberlain's son, Kenneth Jr., calls for Westchester District Attorney Janet DiFiore to charge the officers involved in the shooting with murder and civil rights violations.

"I am sorry for your loss. An outrage of the magnitude of Trayvon Martin," Karen Goodwin of Dover, New Hampshire, wrote on the petition.

Much of the controversy surrounds audio and video recordings made in the minutes before the November 19 shooting.

The medical alert device recorded much of the conversation between police and Chamberlain, according to Kenneth Chamberlain Jr., who said authorities played the audio and video for the family in the aftermath of the shooting.

"You hear one of the officers use expletive and said that he didn't give an F. Used the N-word," he said.

Law enforcement sources confirmed to CNN's Soledad O'Brien that racial slurs are clearly heard on the audio tape.

Chamberlain's niece, Tonya Greenhill, who lived next door, said she heard police banging on her uncle's door that morning.

Greenhill, who has been called to testify before the grand jury, said she told police that her uncle accidentally set off his medical alert device and that they should allow his family to talk to him, to calm him down.

"I continued to hear my uncle begging and pleading to please leave him alone," Greenhill told O'Brien.

"I just keep hearing my uncle respond 'Please leave me alone, go away. I didn't call you. I don't need your help.'"

According to a police report, the officers contend Chamberlain put a hatchet through a gap in the front door as officers were trying to pry it open.

A video tape recorded by a surveillance camera in the hallway outside the apartment, and another recorded by a camera mounted on a Taser -- both shown to the family by the district attorney -- show that he is unarmed, Chamberlain's son said.

Neither video show the shooting. The video from the Taser cut out after it was used.

Police contend they attempted to subdue Chamberlain first with non-lethal force.

"The officers first used an electronic Taser, which was discharged, hit the victim, and had no effect. While the officers were retreating, the officers then used a bean bag shotgun," said David Chong, a White Plains police spokesman.

When that failed to stop Chamberlain, an officer opened fire.

The officer has been identified as Anthony Carelli.

Chong said his office is cooperating with a grand jury investigation, but would not say whether Carelli continues to be on patrol. Carelli's lawyers say he is a decorated officer who followed procedures.

"We trust that the grand jury will rightfully determine that Officer Carelli's actions, while perhaps not understandable or acceptable to the family members, attorneys and other emissaries of the Chamberlain family, were justified under our laws," Carelli's attorney Andrew C. Quinn told CNN in a written statement.

An autopsy report, obtained by CNN, shows the gunshots hit Chamberlain in the side of the arm, indicating he either was not facing the officers or had turned away.

Westchester County is an affluent suburb north of New York City, though Chamberlain lived in a one-bedroom apartment in a public housing project in White Plains -- a commercial hub of roughly 60,000.

"I think that what happened that night is that Mr. Chamberlain happened to live in public housing and we had police officers who gave him a command to open the door and when he didn't acknowledge their command, really became very agitated and angry because he was defying what they asked him to do," Chamberlain attorney Randy McLaughlin said on "AC360."

"They forgot that they were there to deal with a medical emergency. You have here a 68-year-old man who has served this country in Vietnam for six years, and a 20-year retired member of the Department of Corrections for Westchester County who died, but didn't have to die."

The Chamberlains have filed a wrongful death lawsuit against the police department.

The shooting death also prompted Westchester County residents to start a "Network for Police Accountability," which calls on the police department to publicize how and when its officers may use deadly force.