On May 20, 1975, at around 8:15 p.m., Diane Déry, age 13, and Mario Corbeil, age 15, left Diane’s home to go for a motorcycle ride in a field near boulevard Rolland-Therrien in Longueuil. Seeing that the young people had not returned, family members of the two teenagers searched the area during the evening and night.
The next morning, at around 7:20 a.m., the police found the bodies of Diane Déry and Mario Corbeil in a wooded area at the end of boulevard Rolland-Therrien and avenue Vaugeulin. The crime scene analysis showed that the two young people were murdered.
From Allo Police, August 5, 1979 by Jaques Durand
After 4 years and no resolution, the father of Diane Dery, Jaques Dery demanded of the then Quebec Justice Minister, Marc-Andre Bedard that the case be taken away from the investigating force, the Longueuil police, and transferred to the Surete du Quebec.
In 1975 the Derys lived at 1145 rue Bizard in Longueuil. They since moved to Saint-Celestin (Nicolet). He worked at a gas station, his wife ran the small cantine inside.
The parents of Maro Corbeil, M and Mne Maurice and Francoise Corbeil continued to live in Longueuil on rue Boucher. The Dery’s attorney in the affair was Guy Houle.
A recounting of events of May 20th and 21st, 1975, from Allo Police
It was a Tuesday, a beautiful day. Mario’s parents gave him a small motocylette as a present. Mario spent many hours enjoying it, giving rides to his family and friends. The last ride was reserved for a petite ami, Diane Dery. The families would never see them alive again.
The next day, Wednesday, May 21st, the bodies were discovered in a field near the Saint Hubert airport. Mario had been beaten, then shot six times with a 22 caliber pistol. Diane had been shot once in the back of the head with the same caliber pistol, and once in her mid-section. She may have been raped, and her body was placed on top of Mario’s. The bodies were placed in such a way as to suggest they had a sexual relationship.
The case was turned over to lieutenant detectives Lacombe and Villeneuve of the Longueuil police. A dozen persons were interrogated.
After two years, M Jacques Dery made the decision to sell everything and settle elsewhere. The family had a new daughter, Manon, and they wanted to start a better life. He moved to a corner of the province, Saint-Celestin (Nicolet). M Dery became the proprietor of a gas station along route 20. He established a solid clientele. He had another project in mind: getting his entire family out of Longueuil as soon as possible. M Dery bought a house, and in the month of October his family moved to this small, strong and sympathetic village.
The work was hard, it required him to work seven days a week. Not satisfied with her husband working alone, Mme Dery decided to operate a small cantine inside the gas station. Despite the arrangement, there were always two questions that needed answering: WHO and WHY?
M Dery continued to communicate with investigators back in Longueuil. Investigators continued to communicate the same message, “We suspect someone, but we do not have the proof.”
Wanting to know more, M and Mme Dery met with lieutenant-detective Maurice Lauzon, who was the head of Longueuil homicide. He advised the Dery’s that he was not familiar with the dossier, but he would get up to speed quickly. He promised to telephone the family regularly to give them updates on the investigation.
” He never responded at all. I left messages, but he never called back. It was always me that had to telephone”, said M. Dery who added, “If the Longueuil police can’t do anything to advance the case, why can’t they turn it over to the Surete du Quebec? It’s not possible that two young children are killed so close to their homes, and they can’t find anything. It’s not possible, maybe the Surete du Quebec won’t be able to find anything either, but we’d have the satisfaction to know that we tried.”
During the interview, which took place inside the gas station, as M Dery sold cigarettes to customers coming and going, his son pumped gas and Manon rested on the counter. When things settled down the boy came inside, and the children stayed close to their parents.
Mme Dery, who was sitting in the window, said “After four years I’ve come to accept it I know now that she’s never coming back. I accept that, but why would someone do that?”
Through their attorney, Guy Houle, the Dery’s made a request to the Quebec Justice Minister Marc-Andre Bedard to officially have the case transferred from the City of Longueuil police to the provincial police, the Surete du Quebec. Here is the text from M Dery’s request sent through the Dery’s attorney, Guy Houle:
“Honerable Minister of Justice:
Considering the events of May 20th, 1975. my child Diane Dery, age 13, a victim of an assassin, close to our home at 1145 rue Bizard in Longueuil;
Considering that certain actions and enterprises by the municipal police of Longueuil were attempted to elucidate this investigation, but no concrete results were given in the total study of this case;
Considering that now for more than four years we had hoped to see results in these affairs;
Considering that the municipal police of Longueuil, despite all efforts at their disposal, possibly do not possess all the necessary tools to conduct an investigation and achieve results;
Considering above all that the municipal police of Longueuil do not specialize in these types of investigations;
Considering that the Surete du Quebec has at their disposal a homicide squad;
It’s why the people need to be confident in institutions, and certainly in the protection of society against assassins who may walk free among us.
We submit this request to the honorable Minister of Justice of the Province that you will take a hand in this affair jointly with the municipal police of Longueuil to shed a light in the name of justice and public security.”
This letter was sent to the Justice Minister on July 5th. 1979. It was also sent to the Longueuil police, the Deputy of Nicolet-Yamaska, Me Serge Fontaine, and our collaborator at Allo Police, Claude Poirier.
Just as we were leaving Saint-Celestin, the Dery’s young daughter, who up until then had said nothing offered, ” Today people will kill for two dollars; We want justice, and all of them know why they did it.”
The Dery family has suffered. Will they be happy one day when they know the names of the assassins? We hope so.
The Maurice Corbeil family also left their home on rue Boucher in Longueuil. Mme Corbeil moved to Saint-Felix-de-Kingsey, she would like to continue to go to Beauce.
Mne Corbeil has come to an accord with the investigation. Of the police she says, “We were suspected for being suspicious. I want the investigation because in things like this we must find the culprits.” Nevertheless she tries not to think of the horrible things: “I don’t want any publicity for my son, and I don’t want to look at it. Why would you want publicity for such a thing?”
In November 1979, the Justice Minister of Quebec agreed to the families’ requests and transferred the cases to the Surete du Quebec. Diane Dery and Mario Corbeil are currently listed on the Surete du Quebec’s cold case website, still unsolved after 43 years:
Coda: In the La Presse obituary from 1975 it was stated that Diane Dery “died accidentally”, most likely so that the family could avoid shame with the community.