Unemployed waiter Alberto Sanchez Gomez, 26, claims he shocked detectives with the gruesome admission when they came to investigate the disappearance of Maria Soledad Gomez.
Stunned police then made the gruesome discovery of her body parts in six large Tupperware containers near the family home in a flat near the Las Ventas bullring in Madrid.
Shocking details of the horrific crime emerged today ahead of a court hearing in the Spanish capital.
Local reports state the 66-year-old pensioner was cut into at least 1,000 tiny pieces and her vital organs were missing.
It is also claimed that her intestines were found mixed with domestic waste inside the flat.
Although her son is expected to be charged with killing her, police have not yet revealed an exact cause of death.
She was last reported to have been seen sunbathing by a neighbour around a month ago.
As the first photos of suspect Gomez were revealed today, former friends of the alleged cannibal told of how he had a number of problems after becoming addicted to drugs.
It was reported he also used to spend his days hanging out on a park bench near his mum’s flat getting drunk with local homeless people.
Police sources say they believe Gomez, who was one of three children whose dad died when he was 15, cooked parts of his mum’s body and fed them to his dog.
He was known to local cops due to a number of previous arrests thought to be linked to domestic violence incidents against his mother.
She is said to have been seen sporting bruises by neighbours, who thought the injuries were caused by the dog.
Gomez, whose name was released by Spanish media, is undergoing psychiatric evaluation but is expected to be remanded in prison following his court appearance.
A spokesman for the National Police in Madrid said: “A 26-year-old man has been arrested in Madrid for allegedly dismembering his mum.
“Officers have found part of her remains in Tupperware storage containers.
“The victim had been missing for a month.”
A neighbour told Spanish daily El Pais: “Many nights he’d be sitting on a bench in a little square near the flat till two in the morning.
“He seemed out of it as if he was on drugs. He wouldn’t even realise you had gone past.
“He’d steal valuables from his mum and spend the cash on drugs.”
Additional reporting by Natalia Penza.