Unknown people tried to set civic activist Heena Shroff's house in Vile Parle on fire early on Tuesday morning. They hurled lit cloth balls at her windows. Her son, who had woken up at six in the morning, spotted the fire and doused it.

Shroff is known to take on politicians, developers, drug peddlers and criminals in the area. She has received death threats. In the recent past, she has taken on drug peddlers in the area, as well as developers who had encroached on a plot reserved for a school and constructed a residential tower on it.

"She has been active fighting on these issues. She along with other civic activist in K-west and H-west had approached the police over drug peddling in the area. In October last year, Santacruz police had confiscated 13-kg of drugs along with Rs 85,000 in cash from the area. Police had registered a non-cognizable complaint, but did not hand over copy of the FIR to us. We have been demanding action since then, but the police haven't been cooperating with us," said Aftab Siddique, who accompanied Heena, her son, and Niranjan Advani, another activist, to the police station to register an FIR on Tuesday.

Shroff said they expected the police to find the culprit as it was a clear case of intimidation. "My son Akshobh saw the fire as he had happened to wake up just then. The window had caught fire and it would have spread," Shroff, who stays on the ground floor of Park View building on Baptista Road.

Shroff called up the police to report the matter and immediately rushed out to check the whereabouts of the security staff in the building. "To my surprise, the security man on night shift was not in his place. When the police asked him where he had been, he said he had stepped out as he had felt uneasy. But before the police arrived, I had stopped an unknown man from entering the building. He claimed he had come to use the toilet meant for the security staff in our apartment.

The police have registered an FIR under IPC sections 436 (mischief by fire or explosive substance with intent to destroy house), 427 (causing damage to property) and 506 -II (criminal intimidation or deliberate attempt to cause harm or kill).

Satyanarayan Chaudhari, DCP Zone-IX, said the watchman of the building had been arrested.

"Heena Shroff had had an argument with the watchman 10 days ago. He must have done this to teach her a lesson. The police are also investigating whether someone else had taken advantage of the situation to carry out the attack," said a police officer in Santacruz police station. P I Bhimashankar Dhole and his team are investigating the case.