Nine cars were torched in Berlin on Thursday in the third consecutive night of arson attacks that have outraged Germans and drawn condemnation from German Chancellor Angela Merkel.
While arson attacks on luxury cars in Berlin and Hamburg have been relatively common in recent years, the current spate has attracted increased attention in the wake of Britain's recent outbreak of rioting.
Berlin officials say there is no indication of a link, but have few leads on who is behind the nighttime attacks.
"We desperately need tips from citizens," said Rainer Wendt, the head of Germany's police union.
Nearly 40 cars have been set on fire in Berlin over the past three days and police are offering a euro5,000 ($7,180) reward to anyone who helps them find the perpetrators.
"There seems to be an individual, or a small group, setting a lot of fires, and a political intention really can't be seen," police spokesman Thomas Neuendorf told n-tv television.
More than 100 officers are involved in trying to track down the vandal, or vandals, he said.
Merkel, speaking across the country in Wiesbaden, condemned the attacks and pledged her government's support for police.
"What kind of behavior is that _ willingly risking the lives of others?" Merkel asked.
No one has been injured so far in the latest attacks, which hit relatively affluent western Berlin neighborhoods, police said. Cars torched included three BMWs, three Audis, as well as a Ford, an Opel and a Volkswagen.
Wendt agreed that the attacks do not appear to be politically motivated.
"There are other motives, such as the fun of destroying something, and violence," he told news agency dapd, noting that this makes it more difficult for authorities to find the arsonists. In the past, leftist extremists have often been blamed for torching luxury vehicles in Germany's biggest cities.
Berlin Mayor Klaus Wowereit, whose center-left government faces a state election on Sept. 18, has called on residents to help authorities by reporting anything suspicious.
He noted that there are 1.2 million cars registered in Berlin and they cannot all be protected all the time.
"In this case we're poking around a little in the dark," Wowereit said.
Merkel's conservative party, which is trailing in local polls, indicated it plans to make an issue of the car torching in the Berlin election.
"Anyone who wants to govern Berlin must get a grip on violence and vandalism," conservative candidate Frank Henkel said.