Gregory was found, with his hands and feet bound, in the Vologne river in eastern France on October 16, 1984, and it has remained a high profile case ever since, partly because of a series of anonymous poison pen letters which were posted after the murder.
The Gregory Villemin murder: case summary October 1984-May 2017 #AffaireGregory #GregoryVillemin #Gregory https://t.co/fQEO5VDWhO pic.twitter.com/G2mSETuDba
— shadwell (@shadwell_NTT) July 11, 2017
The case was recently reopened and Gregory's great aunt and great uncle, Jacqueline Jacob, 72, and Marcel Jacob, 71, were charged with kidnapping and confinement.
The new investigation highlighted alleged failures made by the original inquiry.
Judge Lambert, 65, is understood to have been extremely upset about the criticism made of his investigation, which he handled until 1987.
On Tuesday, July 11, French news channel BFM, published notes from another judge, Maurice Simon, who had looked at the case and had severely criticized Judge Lambert's work.
Judge Lambert, who was retired, was found dead at his home near Le Mans in north-west France late on Tuesday night.
"There was no trace of violence and no trace of a break-in," said the Le Mans prosecutor.
A month after Gregory's death, Bernard Laroche, who was one of his father's cousins, was charged with murder. Murielle Bolle, his sister-in-law, is now under investigation.
Ms. Bolle, who was 15 at the time of the murder, has always proclaimed her innocence and went on hunger strike recently, ending it on the same day Judge Lambert died.
Mr. Laroche was later freed and exonerated, but Gregory's father, Jean-Marie Villemin, shot him dead in 1985 and served four years in jail for the killing.
After Mr. Laroche was killed, Mr. Lambert began pointing the finger at Gregory's mother, Christine Villemin, who was seen at the post office on the day the letters were sent.
She was accused of carrying out the murder, but eventually cleared in 1993.
Judge Simon wrote that Judge Lambert had an "intellectual disorder" and was perpetrating a "miscarriage of justice in all its horror" against Gregory Villemin's mother.