The accused - Savita Gupta (21), who worked as an assistant to the deceased, her 17-year-old brother, her boy friend Vinay Bose (24) and the latter's friend Gaurank Khawale (21) - were arrested on charges of murder-cum-robbery, police said.
Photographer and short-filmmaker Navraj Kwatra (65) was allegedly strangled to death at his residence on the ground floor in Wilderness Co-operative Society in Borivali last week on September 14.
His wife lives in Delhi, while daughter has gone to Thailand for some exhibition, police said.
According to police, Vinay was in need of money when Savita, who had been working as assistant to Kwatra for the past three months, told him that her boss was generous and always helped people.
However, instead of seeking help from Kwatra, Vinay along with his neighbour friend Gaurank, who works as a courier boy and also needed money for his bike repair, conspired to rob him. Vinay had earlier worked as a cook in some posh hotels in Mumbai suburbs, police said.
On September 13, Savita accompanied Vinay and Gaurank till Borivali railway station.
Vinay and Gaurank then went to Kwatra's house, posing as courier boys but the door was locked, police added.
The next day, the duo came accompanied with Savita's brother, who stood outside the house while the two got access to the victim's house by claiming to be courier boys, police claimed.
The duo then demanded money from him, but when Kwatra raised an alarm, they gagged him and tied his hands.
"The duo then strangulated the senior citizen before decamping with cash of Rs 55,000 and a camera," a police officer said.
However, police did not disclose as to why Vinay needed money and added that they questioned over 100 people in connection with the murder.
Vinay and Gaurank lived in Elphinstone area while Savita and her brother stayed in Worli Koliwada in central Mumbai.