A 52-year-old from Sauerland is said to have first threatened his wife, who lives separately from him, and then intentionally caused a car head-on collision.
The man was in custody for attempted homicide, the prosecutor and the police said.
The prosecutor responsible, Klaus Neulken, said he had previously threatened his wife, who was ten years his junior and who had a new partner, with death.
In the head-on collision on Monday evening in Brilon, the 42-year-old woman and the couple's five-year-old son were seriously injured.
The 42-year-old's new partner, who was sitting in the passenger seat, and the 52-year-old in the oncoming car suffered minor injuries.
"Obviously, the 52-year-old had ended his life, because it's impossible to predict how such a collision will end," said the prosecutor.
The woman's car was completely destroyed.
According to the prosecutor, the suspect had followed his wife in the car for a while, but then disappeared.
After about an hour he suddenly reappeared – from the opposite direction.
An expert will now check how high the impact speed was.
Originally, the police had suspected a traffic accident in the collision.
bbr/dpa