They said the post-mortem exam was performed late on Wednesday, hours after Zeinoun al-Maqari was pronounced dead on arrival at a hospital in Assiut, the closest city to the Al-Muharraq monastery where the monk has lived since last month.
The monk was buried on Wednesday night in St Macarius monastery (pictured below), north west of Cairo, where he joined as a novice more than a decade ago and the scene of the killing of the abbot, Bishop Epiphanius (pictured above).
Zeinoun died a day before he was scheduled to give evidence for the prosecution in the trial of two monks – one of whom has been defrocked – charged with the killing of the abbot.
Hearings were adjourned until 27th October.
Zeinoun was among six monks from St Macarius who were banished to different monasteries across the country as part of disciplinary action taken by the church following the death of Epiphanius.
The officials said questioning of witnesses and monks following his death showed that Zeinoun might have been an accomplice in the killing, but did not explain why he has not been arrested.
The officials said the post-mortem examination showed signs of an agricultural insecticide commonly used in southern Egypt, where al-Muharraq monastery is located.
The insecticide is sold in tablets, which are diluted in water before it is manually sprayed on crops.
