Police in the western French city of Nantes have found a leg under the house of a family of six reported missing for more than two weeks.
Investigators now suspect kidnap and murder to have taken place, city prosecutor Xavier Ronsin said, announcing the find to reporters.
He added that the couple and their four children had kept to themselves.
The parents recently informed a school their children were being removed because of a sudden move to Australia.
There has been no trace of the father, 50, or mother, 49, or their children aged 13, 16, 18 and 21, since the beginning of April, Mr Ronsin said on Thursday.
Records show no internet or phone communications with the house in the centre of Nantes since 3 or 4 April, AFP news agency reports.
Since the discovery of the leg beneath a terrace at the house, the investigation is “leaning towards kidnapping and murder”, Mr Ronsin said.
Before the disappearance, the family left “rambling and contradictory” messages, saying they were taking their two younger children out of school because they were emigrating to Australia.
“The father explained he was a secret agent and was leaving as part of a witness protection programme,” the prosecutor said, quoting people who know the missing man.
No trace of a struggle or violence has yet been found at the house, where the wardrobes have been emptied, he said.
The family were living in a one-storey house on a central boulevard in Nantes, with all its windows shuttered.
A note cellotaped to the letter-box reads “Return all mail to sender”.
A black Golf car, which neighbours say belongs to the mother, stands parked nearby.
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