A glance at the map of incidents explains why: the attacks spatter the inner Roman suburbs like a case of measles, from posh suburbs such as Parioli, home of many foreign embassies, to working-class quarters such as San Basilio, which was struck earlier this week.
"I was sleeping then I woke to find my car in flames," said a resident of San Basilio who works as a stonecutter. "I just bought it a few days ago. I've got to start paying instalments on it in December. I've got two children, I earn less than €1,200 (£830) a month. I've no idea what I'm going to do. My wife's eyes are red with tears."
A neighbour whose car was spared said: "From tonight I'm going to sleep in my car with a stout stick."
The Roman authorities thought they had cracked the problem on 15 July when they disturbed a man in his thirties bent over a Lancia with a bottle of flammable liquid and a lighter. They were so confident they called a press conference to say that the menace, which in two weeks had already seen 54 cars, 43 scooters, four rubbish bins and two shops destroyed, was over.
The man, Alfredo Vitelli, a schizophrenic known locally as "Alfred the Mad", had no previous convictions, and it is still unclear whether he was responsible for some attacks. But when, four nights after his arrest, four scooters and a car in Monteverde went up in smoke, the police realised they had a bigger problem on their hands.
Police are now flying helicopters equipped with floodlights and infra-red video cameras over the city every other night. That is in addition to intensified conventional patrols.
"Despite the terrorism threat, we have mobilised all forces possible," said the commander of Rome's carabinieri. Rome's prefect, Achille Serra, has appealed to citizens for help in the hunt for the attackers. "I'm worried," he confessed, "because I don't think this is the work of a single person."
Two local councillors with Alleanza Nazionale, the right-wing party which is descended from Mussolini's Fascist party, responded to the call by announcing they were forming a vigilante patrol in their neighbourhood.
"There are about 15 of us," said one vigilante. "The idea is to patrol the streets of Marconi and Portuense". The vigilantes can summon help by mobile phone.
But Mr Serra said he was not in favour of the vigilante initiative. "This was not the sort of citizen help that I had in mind," he said.
The police union said that the vigilante patrols "could result in do-it-yourself justice, which does not produce positive results".
In addition to the cost of replacing their car - insurance does not cover deliberately set fires - victims of the attacks must pay the city €90 to remove the "solid urban refuse" to which their vehicle has been reduced, or face a fine of €1,600.Reuse content