St. Louis, MO ( KTRS ) A man who schemed with his ex-wife in a string of arson fires meant to defraud insurers has been ordered to spend nearly six years in federal prison for his role in a 2001 blaze that killed their teenage son.

Steven Kemper was sentenced Monday in St. Louis to five years and 10 months in prison.

Kemper and Sandra Bryant have pleaded guilty to one felony count of aiding and abetting the use of fire to commit mail fraud.

Bryant is to be sentenced next month.

Investigators say the fire at the family’s home suburban St. Louis home killed 15-year-old Zachariah Kemper after he became trapped in the basement he shared with his mother while her mother, Kemper and his lover lived upstairs. All of the adults escaped.