Yet he has never stood trial, let alone been convicted.
A prisoner of his wrecked body and mind, red tape, indifference, poverty, and lax legal representation, Dunn has been condemned to a Waiting for Godot purgatory.
Although his situation is extreme, the small band of advocates who have finally come to his aid say Dunn's experience exemplifies a troubling national trend that has turned prisons into society's psychiatric institutions.
"This is the largest psychiatric facility in Pennsylvania," said Bruce Herdman, director of medical operations for the prison system.
An estimated 45 percent of federal offenders, 56 percent of state offenders, and 64 percent of jail inmates have some sort of mental-health problem, according to U.S. Bureau of Justice Statistics.
Dunn's experience also touches on many of the problems facing the fastest-growing segment of America's prison population - inmates who are aging, alone, sick, and forgotten.
"They're getting older, their neighbors are getting older, their contacts are getting older," said Ann Schwartzman, executive director of the Pennsylvania Prison Society, which never heard about Dunn's case. "We're going to see more people lost in the system because they're losing those links."
In all of his time behind bars, Dunn has had few visitors, and, until recently, no one to advocate for him. The license of the first of his two court-appointed lawyers was suspended in 2010 for neglecting to properly represent clients.
Dunn's isolation was compounded by the fact that he is waiting for a trial that - short of a miracle recovery - will never be held.
"Who knows how many others are out there like Mr. Dunn who have disappeared into the system? There's no systematic way to identify these people," said Common Pleas Court Senior Judge Benjamin Lerner.
The bungling of Dunn's case "doesn't even rise to the level of incompetence," Lerner said. "We are dealing with defendants who are poor and sick, people who have absolutely no voice, no power. There's a million ways of saying no when you try to get somebody some special assistance. It's like trying to line up all the stars."
Those who knew Dunn when he was younger say there is no doubt he was mentally ill.
"He acted weird and was always mumbling to himself," said Adrienne Salley, a longtime neighbor on the 3000 block of Carlisle Street in North Philadelphia.
"He was scary," said Harriett Freeman, another neighbor, who said she knew Dunn and his family well. "He stayed in the house. He had a lot of problems."
When he was in his 20s, according to court records, Dunn pleaded guilty to burglary and theft and was put on probation. In the 1980s, he was charged with illegal gun possession, but the case was dismissed.
He had lived in the white rowhouse in the middle of the block for as long as anyone could remember. His parents, Mary and Charles Ingram, died in the 1990s. The place was falling apart when, in fall 2006, Dunn's brother, niece, and sister-in-law moved in.
In February, Dunn's brother was captured by a bounty hunter and sent to prison in South Carolina.
Dunn did not like living with his sister-in-law. Several weeks before the shooting, he called police to the house and asked them to evict Dozier because she had thrown away a favorite chair, police records show.
At 8:20 on the rainy morning of April 12, Dozier was about to take her stepdaughter to school. According to the girl's statement to investigators, her uncle came up to the driver's side of the red Toyota. They argued briefly about bills and cash, then he took out a revolver and started shooting.
Witnesses said Dozier crawled out of the car, collapsed on the sidewalk, and told the girl to call the police. The ambulance arrived within minutes, and at 8:45 a.m., Dozier was pronounced dead at Temple University Hospital.
Dunn was arrested the next day.
Six weeks later, he had his first stroke.
"When Mr. Dunn was first arrested," Lerner said, "it's my understanding that he had a long history of mental-health issues. . . . He was probably incompetent to stand trial at that time."
In many cases, Lerner said, defendants can be rehabilitated enough to stand trial after a spell at Norristown State Hospital, where they receive medication, therapy, and "competency counseling" - special tutoring to help them understand the legal process.
No one will ever know whether Dunn might have benefited from treatment, however, because the strokes rendered him so deeply and permanently disabled.
Year after year, one judge after another ordered mental and physical assessments to determine Dunn's competence, and year after year, a series of doctors, nurses, and psychiatrists reached the same conclusion.
"After several attempts to communicate with Mr. Dunn with communication boards and pictures, it has been to no avail. Mr. Dunn will respond to most questions with either a yes or no but inappropriately. . . . This condition is permanent. . . . He cannot participate in his own defense."
"It is unlikely that this defendant will be restored to a state of competency during his lifetime."
The one exception was Elizabeth Winters, a doctor employed by the prison's health contractor, Corizon.
In February 2010, in a letter to the court, Winters wrote, "Mr. Dunn remains nonverbal, except for grunting, 'yeah' or 'no.' I am unable to perform standard short-term memory, judgment, and cognitive mental status evaluations on him."
Yet she concluded he was fit to stand trial based on her observations that he used body language, could feed himself "without any choking difficulty," take himself to the toilet, and recognize when it was time to leave the TV room and propel his wheelchair to dinner.
James S. Bruno, his attorney at the time, said that during the subsequent preliminary hearing, Dunn sat in his wheelchair, oblivious to the proceedings.
"It was absurd," Bruno said.
The case never advanced.
"People didn't know what to do," said Phyllis Taylor, a rabbi who worked as chaplain and de facto prisoners' advocate in the Philadelphia prisons. "So much for fair and speedy trials."
The county prison is neither designed nor equipped to house people like Dunn, Lerner said. It is a temporary holding facility for prisoners waiting for trial or serving sentences of less than two years.
"No one," he said, "is supposed to die there."
Dunn has been in the prison longer than anyone else in recent memory, said Herdman, the prison's medical operations director.
In terms of his mental illness, Dunn was not unusual. Of the county's 8,500 inmates, about 35 percent are mentally ill, 15 percent of whom are seriously impaired with schizophrenia, bipolar disease, or psychosis. If you include personality disorders, Herdman said, the percentage would be, perhaps, 80 percent.
Among women, he said, the percentages are even higher. About 80 percent of the women at the county's Riverside facility are on psychiatric medicines, he said, and half have been diagnosed with serious mental illness.
"Nationwide, you will see similar figures," said civil rights attorney David Rudovsky.
"Virtually everybody who has looked at this problem of seriously mentally ill people in prisons agrees that many are there as a result of a lack of mental-health care in the community," Rudovsky said. "Despite the enormous cost of using prisons as the last mental-health catchment area, we don't see much change in the system."
A former senior vice president of Keystone Mercy Healthcare, Herdman, 67, was also a top administrator at Independence Blue Cross and Pennsylvania Hospital. He came out of retirement six years ago to run Philadelphia's prison health-care system.
Of the prison's $227 million budget, Herdman said, $62 million goes for health care.
Dunn has been a particularly expensive inmate.
Herdman estimates the cost of Dunn's care and confinement amounted to at least $60,000 a year.
Given the extent and variety of Dunn's ailments, several observers said, the prison deserves credit for having taken such good care of him for so long.
"Fortunately," Rudovsky said, "he was able to receive medical attention for his numerous conditions while he was at the prison."
Lerner learned about Dunn's condition in December 2013 when Taylor, the rabbi who had been concerned about Dunn for many years, finally found a lawyer willing to help the invalid inmate.
That lawyer, Allan J. Sagot, wrote to the judge: "I thought it appropriate to contact you because . . . his most recent appointed counsel . . . is not visiting him or has any apparent knowledge of his condition."
Ever since, Lerner has been demanding with increasing frustration that Dunn be transferred to a more appropriate setting, either a mental hospital or a nursing home.
He recruited assistance from state officials and the Philadelphia Corporation on Aging and helped arrange a hearing in Orphan's Court so Dunn could be assigned a guardian.
He issued a series of orders and repeatedly threatened to hold those who failed to follow through with contempt of court.
Even so, until recently, each order created a flurry of e-mails and phone calls, but little progress.
The inaction perplexed Lerner, he said, because the court, prosecutors, and prison officials all agreed the move was warranted and long overdue.
(The District Attorney's Office said it could not comment on the case because Dunn is scheduled for a status hearing in December.)
This spring, it looked as though Dunn would be moved at last. His current attorney, Bobby Hoof, was told an ambulance would arrive at the prison infirmary May 28 to transfer Dunn to South Mountain Restoration Center, a state-run nursing home near Chambersburg, Pa.
At the last minute, the date was postponed to June 4. Then it was canceled again. The snag appeared to be caused by some missing paperwork. But last week, Lerner was told the nursing home did not realize Dunn was confined to a wheelchair and did not think he could be accommodated at its dialysis center.
That message prompted Herdman and his staff to investigate other dialysis facilities near South Mountain.
They found several.
"We went from everybody pointing fingers at everyone else saying, 'It's not my job' to everyone saying, 'The important thing is to get it done,' " Lerner said.
On Friday afternoon, Hoof received word that an ambulance would arrive at 8 a.m. Monday to transport Dunn to the nursing home.
"I'm thrilled," Hoof said.
His client, who will benefit the most, is probably the least likely to appreciate the victory.
"Mr. Dunn is the one person who has no idea what's going on," Lerner said, "and what all these people are doing to make his remaining time as comfortable as possible."