Mr Roy (54), who handled some high-profile cases when he headed the Anti-Terrorism Squad of the Maharashtra police, allegedly committed suicide at his residence on Friday.
"Himanshu Roy was a dedicated police officer. He was an asset for the police force. Mr Roy was known for his remarkable investigation skills....His demise is a great loss for the state police force," the governor said in his message.
Chief Minister Fadnavis noted that Mr Roy successfully handled several important cases. "In his sudden death, we have lost a dedicated officer. I share the grief of his family members," Mr Fadnavis said.
Former state home minister and Maharashtra NCP chief Jayant Patil told PTI that he had met Mr Roy at a gym a day before his death. "We spoke for about 20 minutes. When I told him that his skin had darkened, he said it was the effect of chemotherapy. There is a limit to (efficacy of) chemotherapy. It's unending and not easy," Patil said.
Mr Roy was a good officer who never compromised on work, he added.
"When he was diagnosed with cancer, he told me he is quitting his job. I suggested instead he should go on a long leave, and he did so.
"We would speak about his health. He would say sometimes it's good, and sometimes there is pain," Patil said.
Congress leader Radhakrishna Vikhe Patil described Mr Roy's death as shocking. "He was an upright officer and a close friend. His untimely exit is a personal loss to me," Mr Vikhe Patil said.
The special public prosecutors who worked with Mr Roy in prominent cases such as the 26/11 Mumbai terror attack fondly remembered him.
"I always perceived Mr Roy as a strong person who was fond of going to gym. He was suffering from a disease for two years and was fighting against it. Maybe he felt burdened and decided he could not take it anymore," special prosecutor Ujjwal Nikam said.
"Whatever the reasons behind his step, the police department has lost a good officer. He was a gentleman and always treated everyone including junior-level policemen with respect," Mr Nikam said.
During the final arguments in the 26/11 terror attack case, Mr Roy, then the joint commissioner of police, Mumbai crime branch, sat through the entire arguments, Mr Nikam recalled.
Another special prosecutor, Raja Thakre, termed Mr Roy as a "thorough professional".
"He had approached me on several occasions when he was the ATS chief, seeking advice on cases. He would always follow up on each and every important case," Mr Thakre said.
Mr Pradip Gharat, special prosecutor in the journalist J Dey murder case, said Mr Roy could have taken the drastic step because of the unbearable pain he was suffering from, for the last two years.
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