A man who is said to have previously killed his father in Ellerstadt in Rhineland-Palatinate hit four cyclists with a car in Mannheim on Sunday evening.
A 71-year-old cyclist was fatally injured, three other people were seriously injured, the police and prosecutors reported on Sunday evening.
They were taken to nearby hospitals.
The alleged perpetrator is 36 years old.
After the collision with the cyclists, the man is said to have left his badly damaged car behind and fled on foot, according to the police.
Later he jumped into the Rhine.
The police were then able to arrest the man.
He is probably in a mental state of emergency.
A police helicopter and the water police were also deployed in the search for the alleged perpetrator.
The Mannheim police ask for relevant information on 0621/174-4444.