The former Hautes-Alpes territorial intelligence commander was found dead Tuesday at her home in Montgardin, near Gap.
The entourage of Martine Terrier, 57, had not heard from her for several days.
And Monday, the gendarmes had sought to join her after her son, a minor, had been taken into custody in a drug case.
An investigation was then opened for "worrying disappearance".
The gendarmes went to his home Tuesday morning, where they made the macabre discovery after several hours of research.
The body of the ex-policewoman, retired since this summer, was stuck between a French window and a shutter, her head covered with a plastic bag.
A dog leash and an electric cable were wrapped around his neck, said the public prosecutor, Florent Crouhy, confirming information from the released Dauphiné.
"The intervention of a third party is not in doubt," said the magistrate, who opened an investigation for "homicide".
The research section of the Marseille gendarmerie was co-entered with the Gap research brigade and the local Chorges brigade.
An autopsy should take place in the next few days.