A Colombian woman was arrested on Thursday morning, after being identified by the Spanish Civil Guard as the mother of the two-week old infant abandoned in a bin.
The mother is said to be a 37-year-old married woman who already has three children, aged four, five and 11, according to newspaper El Mundo.
The baby was discovered by 29-year-old Rafael Diéguez while he was walking his two dogs early on Wednesday morning when he heard what sounded like an animal inside an underground rubbish bin.
"It sounded like the meow of a cat. There was a cat nearby and I thought another one could have slipped inside," Diéguez told Spanish daily ABC.
He called over a friend of his to help fish the animal out. But when they lifted the lid, they got a shock.
"When we opened the lid, we were stunned. It sounded like the cries of a baby," Diéguez said. "And then there was silence. Alarmed, I called the police."
Civil Guard officers Carlos Rodríguez and Andrés Moyano arrived shortly to the scene. They had to call in firefighters and a tow truck to lift the container.
"You could hear the agonized cries of the child," officer Rodríguez, a father of two, told ABC, explaining how worried he felt as they waited for the service vehicles to arrive.
"The minutes felt like hours. The truck was not coming and the baby had stopped crying. We considered the possibility of going inside ourselves to save him, it was very deep, but we tried to squeeze in and could not fit."
The truck arrived and they were able to tip the bin to empty its contents, finding a backpack on top with the roughly two-week-old baby inside, wrapped in bed sheets and with a baby bottle.
The infant, who has been named Marco by rescuers, was transported to hospital and is now in a healthy condition.
Madrid officials said at a press conference that it was the baby bottle found with the infant that led them to the mother. The bottle had been issued by the Alcalá de Henares hospital and officers were able to search through a list of women who had recently given birth there.
They matched the baby's blood type, A positive, to a birth on June 30th, according to newspaper El Pais.
The mother told officers that she abandoned the baby out of desperation and because she did not have enough resources to support another child.
The woman's husband was also taken in for questioning, but was later released because they determined he had nothing to do with the baby's abandonment. The father has now been left to care for the other three children.
The infant will remain in the care of city authorities until he can be placed in a group residence or with a foster family.