The teenager, who allegedly murdered his grandmother with the help of his childhood friend, broke down before the police and confessed to the crime.
The brutal murder by the 16-year-old - who was arrested on Monday - left his parents, who were present in the interrogation room, completely shocked.
"When the parents saw their son confessing to the crime and explaining how he executed it, they were left shell-shocked," said a Crime Branch official, who was present in the room where the minor was grilled.
"The parents could not believe what their son was saying and did not utter a single word," he added.
The victim, Sarla Patel (68), was found in a pool of blood in the bedroom of her flat in suburban Malad on Friday.
Gold ornaments and foreign currency collectively worth Rs 5.14 lakh were stolen from the flat, police said.
On Monday, her teenage grandson and his friend, both studying in separate colleges, were arrested. The entire cash and valuables robbed by them were also recovered, police said.
"The duo was today produced before a juvenile court, which remanded them in judicial custody for one day. They were taken to a remand home in south Mumbai's Dongri area," said Avinash Jadhav, Senior Inspector at Malad police station.
Though investigators were convinced that it was an insider's job - there was no forced entry into the house - they zeroed in on Sarla's grandson when he claimed he did not come home on Friday afternoon, a statement contradicted by the building's watchman.
The duo told police they were in need of money to fulfill their wishes to buy a bike and splurge on 'hookah' and pool parlours.
"The watchman of the building stated the boy had come home in the afternoon. But the accused stated that he had gone to the college and upon returning home at 6.00 pm, he came to know about his grandmother's murder," said the official.
"We waited till Sarla's funeral was over. The teenager looked fine during the funeral and there was no change in his behaviour at all. After the rites, we started grilling the boy," he said.
According to police, Sarla's husband Ramanlal and daughter-in-law Bhavna had gone to a hospital, leaving the victim alone at home on Friday.
Realising Sarla was alone, her grandson, accompanied by his friend, went to the house after buying a nylon rope and surgical gloves in the afternoon, Roy said.
"Sarla allowed the two inside the home and gave them water. After a while, she went into the bedroom. The two followed her inside the bedroom, where they strangled her. Realising she was not yet dead, they slit her throat," police said.