In a jail cell interview aired on Globo television's Fantastico program, 30-year-old bricklayer Roberto Carlos Magalhaes said he mixed water with wine to dope the child before he and his lover held the boy down and stuck sewing needles into him.
"I did this two or three times a week during one month," Magalhaes said.
The boy was too drunk on the wine mixture to cry while he inserted the needles, he said, but felt the pain after the alcohol wore off.
"It was truly an unbearable suffering," said Magalhaes. "It was to get back at the boy's mother. I thought the needles would work their way through his body and kill the boy. It was a way to kill without anyone discovering."
But the pain led the toddler to complain to his mother, and on Dec. 10 she took him to a hospital where X-rays revealed about 30 needles lodged throughout his body.
The boy underwent a five-hour operation in the northeastern city of Salvador on Friday to remove four rusty needles that most threatened his life, near his heart and in his lungs.
Doctors said Sunday the child is doing well and will likely undergo two more surgeries, the next one on Wednesday at the earliest, to extract needles up to 2 inches (5 centimeters) long from his abdomen and spine.
Suzy Moreno, a spokeswoman for Hospital Ana Nery, said hundreds of people across Brazil have contacted the facility to inquire about the boy.
"Many people are coming by to bring Christmas presents," she said. "Many are also calling us to express their outrage. ... The support has been incredible."
Along with Magalhaes, police believe his lover, Angelina Ribeiro dos Santos, was also seeking revenge on Magalhaes' wife.
The bricklayer told detectives that dos Santos would enter into trances and give him commands to insert the needles, police inspector Helder Fernandes Santana said.
Magalhaes and dos Santos were both arrested, though no charges have yet been filed. They were taken to an undisclosed location for their own protection after a mob threw stones at the police station where they were being held.
Dos Santos is not believed to be a member of any religious or occult group, and authorities believe the pair came up with the idea on their own.
The boy's name is not being released because of his age.