Police have set up a dedicated tip-off email address after the latest in a spate of firebomb attacks in Greenock.
One man has died, three homes have been damaged and a car has been burnt out in the past three weeks.
In the latest incident, a flat in the town's Kincaid Court was badly damaged after an accelerant, possibly petrol, was used to set it on fire on Monday.
Detectives are "pleading" for information which can be emailed to OperationTell@scotland.pnn.police.uk.
The trouble began on 14 September when a 46-year-old man named locally as George Miller died at a property in Union Street.
CCTV footage later circulated on social media apparently showing a man accidentally setting himself on fire behind the same property.
Police have not commented on the video but said at the time they were not looking for anyone else in connection with the fire.
Two days later, on 16 September, a woman was badly burned when a flat in Wellington Street was firebombed. Her nine-year-old daughter who was in the property at the time was unhurt.
A white Suzuki Splash car, matching the description of a car seen driving away at speed, was abandoned in nearby Skye Street and was later found ablaze in the early hours of the following morning. The car had been stolen the previous day.
On Saturday 19 September, a suspected petrol bomb was thrown at a house in Cumberland Road but failed to smash the window. A 45-year-old woman, a six-year-old child and two other people inside the house were uninjured, but garden furniture caught fire.
The latest attack, on a flat in Kincaid Court, took place at 22:25 on Monday.
Three men were seen running from the flat and driving away in an electric blue-coloured car, possibly a BMW. The same car had been seen near the flat 30 minutes earlier.
APPEAL FOLLOWING WILFUL FIRERAISING IN KINCAID COURT- Around 10.25pm on Monday, 28 September, we were called to reports of a fire in Kincaid Court, it is believed this fire was set deliberately, possibly using petrol as an accelerant. READ MORE https://t.co/PEv3HzVTsi pic.twitter.com/XXaUq2PgMc— Inverclyde Police (@GreenockPolice) September 29, 2020
Det Supt Gerry McBride said: "This is yet another despicable and reckless act of wilful fireraising in our community, and whether linked to previous incidents or not, I would like to reiterate that this behaviour will not be tolerated.
"Thankfully, nobody was within the property when it was set alight, and residents in neighbouring flats were evacuated and did not come to harm.
"However, this was a targeted attack which could have resulted in serious injury and we will do everything in our power to find those responsible."
He added: "I am pleading to those in the community who might have information to please come forward and tell us what you know."