Mansukh Hiren, who was in possession of the car that was found with explosives outside industrialist Mukesh Ambani's residence, in a letter to Maharashtra Chief Minister and Home Minister had alleged that he was being harassed by police and media.
He had also claimed that in spite of being a victim, he was treated as an accused.
The car, a Scorpio, with 20 gelatin sticks inside was found near 'Antilia', Ambani's multi-storey residence in south Mumbai, on February 25. Police had said the vehicle was stolen from Airoli-Mulund Bridge on February 18.
Hiren, 46, was found dead in a creek in neighbouring Thane on Friday morning.
The Maharashtra Anti-Terrorism Squad has taken over the probe into the entire matter.
A letter dated March 2, purportedly written by Hiren and addressed to CM Uddhav Thackeray, Home Minister Anil Deshmukh and police commissioners of Thane and Mumbai, surfaced on Saturday. The letter had the receiving stamp of the "Commissioner of police, Brihanmumbai" dated March 3.
In the letter, Hiren claimed he was being harassed despite not having any knowledge about the culprits, who not only "stole his vehicle but also misused it".
"I have already given my explanation and statements about how the vehicle was stolen, and I am being victimized and suffering harassment by police and news reporters," Hiren said in the letter.
He sought protection and intervention of the authorities to whom the letter was addressed.
In the letter, Hiren said he had lodged an FIR with Vikhroli police on February 18 about his missing vehicle.
"On February 25,policemen from the ATS told me that the vehicle was found near Ambani's house with explosives. I was interrogated and they left," he said in the letter.
Officials from Ghatkopar police questioned him again on February 26, he said.
Later, officials from Vikhroli police questioned him and detained him at the police station till the next day early morning, after which he was dropped at his house on February 27, he said in the letter.
Hiren mentioned that he also got calls from Vikhroli and Ghatkopar police stations the same day.
On March 1, he was called by the Nagpada ATS, he said.
Hiren also said he was interrogated by (Mumbai police officer) Sachin Vaze at the Crime Intelligence Unit's office and asked the same questions.
He also claimed that he was questioned by "NIA officers and by Joint CP Bhamre".
"The interrogation by various agencies disturbed my peace of mind. In spite of being a victim, I am treated as an accused. I have also been receiving calls from media houses who have been harassing me and my family," he said.
Hiren in the letter also requested for necessary legal action into the matter.
The viscera of Hiren has also been sent for forensic analysis, police said on Saturday.
The autopsy report of Hiren reserved the opinion on the cause of death, officials earlier said.