Some people with "vested interests" targeted Mumbai police without knowing anything about the investigation, he told PTI.
The AIIMS medical board on Saturday stated that Rajput died by suicide and it was not a murder.
Reacting to the news, Singh said the city police's probe was professional, and doctors at the Cooper Hospital in the city who performed autopsy had also done their job thoroughly.
"We all stand vindicated by these findings of AIIMS," the police commissioner said.
The Supreme Court had upheld transfer of the FIR lodged by Bihar police in the Rajput case and not the Mumbai police's investigation, Singh said.
"The court didn't find any fault with our investigation," he said.
Singh further said that the city police had submitted investigation report to the apex court in a sealed cover and it was seen by only six persons -- the investigating officer, senior police inspector, deputy commissioner of police, commissioner of police, advocate general of the state and the judge.
"Without knowing anything about our investigation and without having seen our report some vested interests criticized our investigation," he said.
Rajput (34) was found hanging at his flat in Mumbai on June 14. A section of media had hinted that it could be a murder.
The CBI had taken over the probe from Bihar Police into the alleged abetment to suicide case filed by the actor's father K K Singh in Patna against Rajput's girlfriend Rhea Chakraborty and her family.
(Only the headline and picture of this report may have been reworked by the Business Standard staff; the rest of the content is auto-generated from a syndicated feed.)
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