PARIS -- The brother-in-law of a missing French couple has confessed to killing them and their two adult children with a crowbar, then dismembering the corpses, over an old inheritance dispute, authorities said Monday.

The prosecutor in the western town of Nantes said at a news conference that Hubert Caouissin told investigators he slipped into the home of the Troadec family at night last month with the intention of retrieving a key, but found himself face to face with his brother-in-law, who the suspect said was holding a crowbar.

Caouissin told investigators he managed to wrest the iron bar away, and that he first killed Pascal Troadec and his wife, Brigitte, then their two children, aged 21 and 18.

This handout photo provided by the French Police Nationale sent to French police authorities on Feb. 24, 2017, shows portraits of the missing Troadec family. From left, father Pascal Troadec, mother Brigitte Troadec. AP

“It seems that the bodies were dismembered, that one part was buried, the other part burnt,” prosecutor Pierre Sennes said.

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The prosecutor spoke of a “criminal scene of great violence.” The bodies have not been found so far.

The motive behind the four killings allegedly was a family dispute over a poorly shared inheritance, including gold coins, Sennes said

Caouissin and his partner, Lydie Troadec - the sister of Pascal Troadec - are being questioned by investigating judges and are expected to be handed preliminary charges later Monday, the prosecutor said.

Traces of blood from Pascal and Brigitte Troadec, and from son Sebastien, were found on the staircase and ground floor during an initial search Feb. 23 of the home in Orvault, a suburb of Nantes. The national health card of their 18-year-old daughter, Charlotte, was found in a pair of trousers in a ditch more than 270 kilometers (170 miles) away.

The family phones have gone unused since Feb. 17.