The bodies of Ms Upadhyay, 43, and Mr Bhambhani, 65, were recovered from a drain in suburban Kandivali on Saturday night with their hands and feet tied with ropes, police had said.
Three days after the Mumbai police recovered the bodies of artist Hema Upadhyay and her lawyer Harish Bhambani, covered in plastic, stuffed in cardboard boxes and dumped in a ditch, the police have claimed a breakthrough in the investigation.
Police in Uttar Pradesh have arrested one suspect, Shiv Kumar Rajbhar, in Varanasi district with 20 debit cards, nine of which belonged to Hema and Harish.
"We found about 20 debit cards on the accused when we arrested him from Varanasi. Some of them belong to Hema and Harish. He will now be handed over to the Mumbai police," Uttar Pradesh police officer Sujay Pandey said.
Police in Mumbai have detained three others in connection with the case, including Chintan Upadhyay, Hema's estranged husband. In 2013, Hema had filed a case of harassment against him with Harish Bhambani representing her. Chintan has been detained by the police for over 24 hours now.
While the motive behind the double murders is still unclear, police are still on the lookout for an individual named Gotu, the owner of the warehouse in Kandivali where Hema stored her artwork and with whom Hema allegedly had a dispute over Rs 5 lakh.
Police have also questioned a pickup truck driver, who confirmed that he dumped the two boxes in a drain in Kandivali on Saturday afternoon thinking that it contained broken antiques.
They have recorded the statements of the watchman at Hema's apartment in Juhu Tara Road and her domestic servant Lalit Mandal.
Friends and family members present at Hema's funeral were still unable to come to terms with the brutal murders.
"It is just something that is so bizarre that there are no words to describe one's feeling. She certainly has never ever expressed to me that she was scared for her life," said Shireen Gandhy, owner of an art gallery and a friend of Hema.