Max Shacknai, the son of multimillionaire pharmaceutical tycoon Jonah Shacknai, died at a San Diego hospital yesterday as a result of the fall.
Two days after the accident his father's girlfriend, Rebecca Nalepa - who was looking after him at the time - was found hanging naked from a second-storey balcony, her hands and feet bound with orange electrical cord.
Reports of a party, which would have taken place as Mr Shacknai and his ex-wife held a vigil at their son's bedside, deepen the mystery surrounding the two deaths at the historic Spreckels Mansion in the upscale Coronado suburb of San Diego.
Last Monday, Max fell down the stairs at the property in what police called a tragic accident. He was not breathing and did not have a pulse when paramedics found him.In a joint statement issued last night, his parents announced that the little boy died at Rady's Children's Hospital in San Diego yesterday, and a memorial service will be held today.
The death of 32-year-old Miss Nalepa, described by police as 'very bizarre', came just two days after the fall.
Mr Shacknai's brother, Adam, who was staying in the mansion's guesthouse, cut her down to try and save her then called 911. Mr Shacknai was not at home, police said.
Adam told detectives he found her hanging by her neck from a second floor balcony, with her hands and feet bound.
Firefighters tried to revive Miss Nalepa, who they described as being 'in distress', but she was later pronounced dead at the scene.
Detectives are still waiting for forensic test results to help determine whether Miss Nalepa committed a ritualised suicide or whether she could have been murdered.
Now police have told Mail Online that they are taking another bizarre twist seriously.
Despite the fact that the victim was found bound at her hands and feet, Sergeant Frank said police have not ruled out suicide.
One theory being examined is that she was overwhelmed with grief after the accident involving her lover's son.
But investigators have not established a formal connection between the two tragedies. Sergeant Frank said officers were carrying out interviews with witnesses and waiting for forensic tests.
Rebecca, who has a past conviction for shoplifting, had given up her job as an ophthalmic technician in December to devote her time to Mr Shacknai, Max and his other two children.
She was discovered naked, hanging from a second-storey balcony with her feet and hands bound with orange electrical cord, police have revealed.
While an autopsy has been completed, police are not releasing the details and have not yet ruled whether her grisly death was murder or suicide.
Rebecca, who had been in a relationship with Mr Shacknai for two years, was reportedly looking after the little boy at the time.
The mystery surrounding her death, which police have described as 'bizarre', deepened as it emerged a loud party had been held at the 27-room house on Tuesday night, the day before she died - and the day after the little boy's accident.
Police said Adam Shacknai is not currently being considered a suspect, although he was the only other person believed to have been in the 27-room mansion when Miss Nalepa died.
Both brothers and Mr Shacknai's ex-wife Dina, who is six-year-old Max's mother, are being questioned by police as witnesses.