(CNN) Cedric Willis spent nearly 12 years in prison for a crime he didn't commit. Since his exoneration in 2006, he worked as a motivational speaker, helped register Mississippi residents to vote and visited schools talking about his experience.

"He'd been working out, he was feeling good," says Emily Maw, his attorney with the Innocence Project New Orleans (IPNO). The two had become good friends and Maw says the last time she saw him three weeks ago, "things seemed to be going so well for him."

On June 24, Willis was shot and killed in his Jackson, Mississippi, neighborhood, two blocks from his home.

The Jackson Police Department is investigating Willis' death as a homicide, spokesman Sgt. Roderick Holmes said. Police haven't made any arrests in the case, he said.

"Investigators have interviewed several individuals as it relates to information gathering, but no suspects have been identified," he said. Holmes also said the motive remains unclear.

His mother, Elayne Willis, said police visited last week and told her the incident is still under investigation.

"The only thing I know for certain is my son is dead. He left home and he didn't come back," she told CNN. "I don't know what, why, I don't know anything."

Willis was failed by the country again and again, Maw says.

"America hurts black men in so many ways. Two of the main ways it does that is through the criminal justice system and the utter failure to control guns. Cedric has been a victim of both and that's particularly tragic."

DNA evidence, mistaken eyewitnesses

In the summer of 1994, Willis was 19 and celebrating the birth of his son, CJ, when he was arrested and accused of the rape of a woman in one armed robbery and the murder of a man in another in Jackson.

The two robberies, and three others committed in Jackson at the time, had similar patterns and evidence showed the same gun had been used. Victims gave similar descriptions of the perpetrator, IPNO said.

The suspect, victims said, had a gold tooth and no tattoos, IPNO said, but Willis had no gold teeth and his arms were inked. He was also 70 pounds heavier than their descriptions, according to IPNO.

But victims from both robberies later identified Willis as the perpetrator.

Testing determined his DNA did not match the sample found on the rape victim and prosecutors dropped those charges, but he was tried for the second robbery and murder.

At trial, the jury did not hear about the DNA testing that excluded Willis from one robbery and the rape.

"Eyewitnesses are so often wrong. If you've excluded forensics that point in another direction from eyewitness identification, that's an enormous red flag," Maw said.

Cedric Willis and IPNO attorney Emily Maw

Willis was convicted of murder and armed robbery in 1997 and sentenced to life in prison plus 90 years, according to the Life After Exoneration Program (LAEP).

"They knew they had the wrong man and they prosecuted him any way," Maw said.

Willis was taken to the Mississippi State Penitentiary, where he was kept in solitary confinement for four years, according to the National Registry of Exonerations , which compiles information about exonerations.

His time in prison, Maw says, was especially difficult because he suffered from epilepsy and often had blackouts and seizures.

Willis' request for a new trial went ignored for years, the registry reports.

IPNO heard about WIllis' case in 2004 and in 2005, after the nonprofit law office's request, he was granted a new trial.

"Cedric was very shy and very wary," Maw says of when the two first met. "He'd come to the point where he didn't really trust or believe anyone remembered that he was there except his mom and his family."

"It took a while for him to trust that we were going to stick around and get this done," she said.

In 2006, a judge found previous witness testimony inadmissible, according to the Northwestern University Pritzker School of Law, and the charges against Willis were dismissed.

On March 6, 2006, he became a free man.

A 'very low-key guy'

Willis' mother never believed he committed the crimes and always hoped he'd be free again.

"He had just become a father, he's not going out and killing anybody," she said of the summer when he was arrested.

While he was in prison, Habitat for Humanity built Elayne Willis a house and she insisted they add one more bedroom for her son.

"I told [them] my son was coming home and I've got to have a room for him," she said.

That bedroom is where Willis lived after he was freed and until he died.

In the years since his exoneration, he built a strong relationship with his son and family, and even though his epilepsy often got in the way of keeping a job, Willis kept busy.

He spoke with the NAACP, Maw said. He worked with the ACLU, registering people to vote, doing what he loved to call "election protection," the attorney said. He helped take care of his cousin's and sister's kids, took on a few jobs periodically and, more recently, was enjoying his new role as a grandfather.

"He was just a kindhearted, loving person trying to help people," Elayne Willis said.

His mother says his wrongful conviction had deeply affected him, but he "never ever let it show."

"He was a very low-key guy dealing with an awful lot: the unimaginable wrong and pain he suffered and the difficulty of being a black man in Jackson, Mississippi," Maw says.

Willis was on his way home when he was killed, his mother said.

"He gave me so much joy," she said. "And I'm just going to miss him."