The unemployed Alabama man, who killed his mother and nine others on a vicious shooting rampage, made a list of people who had done him wrong and stocked up on survivalist gear, officials said on Wednesday.
As investigators pieced together the carnage left by the worst shooting spree in the southern state's history, a portrait began to emerge of a troubled, out-of-work loner with a penchant for shooting off guns in his backyard.
Michael McLendon, 28, gunned down his mother and her three dogs, set his house on fire and then tore off on a three-town trail of destruction that finally ended when he fired his gun into his mouth at a factory where he once worked.
The Alabama Bureau of Investigation said late on Wednesday there had been "very recent developments that we believe may direct us to a motive" for the grisly crimes.
Investigators examined the house where McLendon and his mother lived and found a notebook that contained a list of former co-workers of his, as well as an account of grievances, Coffee Country District Attorney Gary McAliley told AFP.
"On his chest of drawers was a list of people he worked with in Kelley Foods," said McAliley, referring to a sausage factory where McLendon worked from July 2007 until he quit suddenly last week.
"And under that a list of things that people who he worked with had done wrong toward him, like 'reported me for not wearing earplugs,' and 'so-and-so made me spend four hours cleaning out the meat grinders,'" said the district attorney.
McAliley added that investigators had interviewed factory workers, none of whom were among the shooting victims, and had found it difficult to corroborate the shooter's claims.
Neighbors and co-workers described McLendon as a quiet type who few people knew well.
"Every neighbor we talked either didn't know him because he was so quiet and secluded, or if they did know him they said he is shy. The only gripe was that he was always in his backyard firing a weapon," said McAliley.
A spokesman for Kelley Foods described him as a "reliable team member" who "just did his job."
McAliley said the family's economic woes were apparent -- on the kitchen table was a letter informing his mother that she had been laid off from her job at a chicken processing plant.
The gunman had made "a list of several pages of bills that they had to pay, and it was obvious he was making notes on which order he wanted to pay," said McAliley.
"I think economics could have been part of it. He was mad at the world somehow."
The Alabama Bureau of Investigation said it "has in its possession all evidence collected from the scene of the first event," which according to the district attorney included a vast cache of military and survivalist gear.
Picking through the partially burned out house where mother and son lived in the small town of Kinston, police found that McLendon had shot his mother in the head, shot her three small dogs and arranged them around her body before covering her with blankets soaked in paint thinner and torching her.
Investigators also uncovered "20-40 ammunition boxes on the floor spread from his bedroom to the living room, a tremendous amount of medical supplies in military bags, many items a survivalist would use," the district attorney said.
Sleeping bags, water-filled canteens, cooking utensils, bandages and a backpack filled with supplies were also found in the house, where McLendon left them before going out and killing neighbors and strangers alike.
McLendon, who was briefly employed as a police officer in 2003, drove to the nearby town of Samson, where he shot his uncle, two of his cousins, and the wife and 18-month-old daughter of local sheriff's deputy as they were on the uncle's front porch, police said.
He then walked next door and killed his 74-year-old grandmother.
Police said the shooter then moved on, killing a pedestrian, a woman at a service station and a man driving his car.
The police chase took them to the Reliable Metal Products factory just north of the town of Geneva, where more shots were fired before McLendon fled inside. Police said they found him dead from a self-inflicted gunshot.
Local media said McLendon had worked in the past at Reliable Metal, though it was unclear when or if he had been fired or laid off.
"What motivates a person to do that?" McAliley asked, pausing to hold back tears. "It is hard to figure out what goes on in the mind. But he has displayed his internal thinking by his conduct."