The fire happened very early Tuesday morning.
It happened in Montevideo on Monday.
She had just graduated from Montevideo High School.
The police say they responded to a "motorcycle collision and fire."
Adam Christopher had been the police chief since 2006.
Montevideo is 130 miles west of the Twin Cities in western Minnesota.
The 18-year-old woman has taken out a restraining order against him.
A man was dead inside a home and a woman injured outside.