BONN, Germany (AP) _ Police are investigating whether an extortionist demanding millions from Daimler-Benz struck again Sunday by hurling a stone from a bridge at a passing Mercedes.

The car avoided the cobblestone, tossed from a bridge at a highway exit near Dorsten in western Germany, but crashed into a guardrail. The driver was uninjured.

A police spokesman said the person who threw the stone escaped, and no letter was left behind.

The carmaker confirmed Friday that it had received letters from someone threatening to toss rocks at Mercedes cars unless it paid a ransom of several million dollars.

One car was hit this month on another highway, also in western Germany. No one was hurt, but investigators say the extortionist left behind a letter saying: ``Next time a driver dies.''

The extortion attempt is the third this year against Daimler.