An autopsy carried out on four of the dead prisoners revealed traces of a lethal substance that had caused heart attacks in some of the victims and severe asphyxiation in the others, Chad's chief prosecutor said.
A group of 44 suspected members of Boko Haram, arrested during a recent operation against the militant group, have been found dead in their prison cell, apparently poisoned, Chad's chief prosecutor announced on Saturday.
Speaking on national television, Youssouf Tom said the 44 prisoners had been found dead in their cell on Thursday.
An autopsy carried out on four of the dead prisoners revealed traces of a lethal substance that had caused heart attacks in some of the victims and severe asphyxiation in the others, he said.
They dead men were among a group of 58 suspects captured during a major army operation in around Lake Chad launched by President Idriss Deby Itno at the end of March.
"Following the fighting around Lake Chad, 58 members of Boko Haram had been taken prisoner and sent to Ndjamena for the purposes of the investigation," said Tom.
"On Thursday morning, their jailers told us that 44 prisoners had been found dead in their cell," Tom said, adding that he had attended the scene.
"We have buried 40 bodies and sent four bodies to the medical examiner for autopsy."
An investigation was ongoing to determine exactly how the prisoners had died, he said.
Major operation against Boko Haram
Earlier this week, Justice Minister Djimet Arabi told AFP the captured men had been handed over to the court system on Wednesday and had been due in court for trial on Thursday.
The military operation against Boko Haram killed more than a thousand of the group's militants and cost the lives of 52 soldiers, a Chadian army spokesman said. The operation ran from March 31 to April 8.
It was launched in response to a devastating attack on Chadian troops on March 23 on a base at Bohoma, in the Lake Chad marshlands, that killed 98 soldiers.
It was the largest one-day loss the army has ever suffered.
Since then, Idriss has warned his allies in the region that Chad's army will no longer take part in operations outside the country.
The force, considered one of the best in the region, has fought Boko Haram in the Lake Chad region as part of the Joint Multinational Force with Nigeria, Cameroon and Niger.
But on Friday, French Defence Minister Florence Parly said Chad remained committed to the G5 Sahel anti-militant force operating in the region.