Sharma further claimed that he had overheard three passengers in his cab talking about keeping three bombs at the site to kill the MNS chief, police said.
On the day of the rally, Thackeray had visited Siddhivinayak Temple in Prabhadevi area seeking blessing before starting the procession from Girgaon to Azad Maidan. Later, he held a rally at Azad Maidan.
Sharma had stated that the trio had discussed about keeping the bombs at these three sites, police said adding that an alert was sounded immediately for security agencies that extensively searched for suspicious objects.
As nothing suspicious was found, cops subsequently tried to contact Sharma on his phone, but it was switched off.
"While checking the police records, it was learnt that Sharma had also made such call on August 4 stating that he had seen 15 to 20 people wielding swords on Service Road area in suburban Khar. As the cops rushed there, they could not find anybody suspicious."
Concluding that Sharma made prank calls, an FIR was registered against him at the Azad Maidan police station, police said.
Police's attempts to trace Sharma failed as he stopped using the SIM card after making the fake call. Acting on a tip-off, a police team probing the case laid a trap and arrested Sharma from Vile Parle.