The close-range gunshot blast tore away skin and exposed tendons and ligaments on the hand that Horton relied on to make a living as a freelance news photographer.
Emergency-room physicians at St. Joseph's Hospital gave Horton morphine to diminish the pain. X-rays showed innumerable bullet fragments throughout his left forearm.
The doctors cleaned the wound and did the best they could to close it with gauze. Little more could be done at the time because of the lack of skin to cover the wound. Horton was given a sling and advised to keep the arm elevated.
Doctors also gave him the name of an orthopedic surgeon to see the next day to begin the long, complicated series of operations necessary to rebuild his shattered hand, medical records show.
But Horton has never gotten a chance to see the specialists. Instead, he has been shown Maricopa County Sheriff Joe Arpaio's jail system.
Horton, 40, was shot by his former girlfriend while trying to enter her home. Now charged with assault and burglary, Horton doesn't deny committing a "stupid" offense.
But he does wonder why he can't get medical treatment for his shattered hand.
Three months after his arrest at a hospital on August 31, Horton has a left arm that is useless.
"The last 12 weeks have been truly horrifying," Horton said in a jailhouse interview last week.
Rather than remove the bullet shards from his forearm, jailhouse doctors have done little but clean the wound, Horton says.
After his swollen hand oozed pus for six weeks, he says, blotches of white scar tissue slowly spread over the wound. Pellets are clearly visible beneath the scarring.
The Ace bandage that holds gauze against the wound hasn't been changed in months and frequently smells foul, he says. Horton says he cleans the bandage in his jail-cell sink, using shampoo as a disinfectant.
"I'll probably be permanently crippled because of what's happened to me," Horton says.
Horton claims he is just one of many of the county's 6,000 inmates and pretrial detainees who are receiving poor medical treatment. Complaints about inadequate medical care are part of an investigation into jail conditions by U.S. Attorney Janet Napolitano.
Bob Bartels, deputy chief of the civil section of the U.S. Attorney General's Office in Phoenix, says the investigation has received information from the Maricopa County Public Defender's Office concerning jail inmates who may have received inadequate medical treatment.
Horton's mother, Shirley Melich, has traveled to Arizona from her Florida home twice in the past three months, attempting to obtain better medical care for her son. So far, she's been unable to even get a doctor to respond to her numerous calls.
"I think it's atrocious he hasn't been given medical care for that hand," she says. "You can look at it and see that it needs care. It has 50 or 60 pieces of metal fragments in his hand."
Horton's public defender, Stephen Rempe, says his client is being abused by the lack of timely medical treatment, but there is little his office can do to force treatment.
"This is the worst I have seen recently," Rempe says.
Rempe says he's trying to reach an agreement with county prosecutors to allow Horton to plead guilty to attempted burglary and credit him with time served since his arrest. Horton's trial is scheduled for Tuesday.
A Sheriff's Office spokesman, Sergeant Tim Campbell, says Horton's medical treatment is determined by doctors at the jail's infirmary and at Maricopa County Medical Center's jail wing.
"If any doctor in there feels he needs more medical treatment, then he will get it," says Campbell. "He's never going to be denied any kind of medical care."
Indeed, Horton has had regular visits to jail doctors in the past three months; during that time, he has spent 18 days in the jail infirmary. Horton says the doctors have given him conflicting advice.
One doctor, Horton says, wanted to operate on his wrist to remove the bullet fragments. But the recommendation was overruled by another doctor, who, Horton says, suggested he go back to the county hospital once he gets out of jail and is enrolled in the county's indigent medical-care system.
Last week, Horton says, a doctor told him to begin vigorously exercising the hand and rotating the wrist to regain flexibility. But other doctors told him to keep the arm immobile because the remaining bullet shards could damage nerves and tissues.
"I get completely opposite advice," he says.
While Horton is protesting his medical treatment, he isn't screaming that he was wrongly arrested.
"I know what I did, and I did a stupid thing," he says.
Horton was incarcerated after he was shot by his former girlfriend; at the time, he was trying to break into her house. The ex-girlfriend had obtained an order of protection preventing Horton from visiting her at home or going to her place of work.
Horton says he was severely depressed and suicidal that evening; he wanted to retrieve a gun he had given his ex-girlfriend several years before. Instead, he received a gunshot wound to his hand and a trip to the county jail.
Horton, who recently returned to Phoenix from Florida, has no immediate family in the area. His freelance photography work and his relationship with his girlfriend both hit the skids about a year ago. There is no way he can post $23,600 bail to get out of jail, given his $800 monthly income, he says.
So Horton, who has no prior convictions, remains incarcerated with 2,500 other, mostly poor detainees who also can't post bond prior to trial.
There is an ironic subtext to Horton's predicament: Sheriff Joe Arpaio's jail once provided part of Horton's living as a news photographer. He photographed Arpaio for USA Today two years ago, when the sheriff erected the now-world-famous Tent City jail.