Anti-persecution charity Christian Solidarity Worldwide (CSW) has been told that Fr John Adeyi may have died because he was unable to access medication after he was abducted.
His decomposing body was found on in June in Benue State, south Nigeria.
Fr John Adey was abducted on 24th April.
He was vicar of St Bernard's Catholic Diocese of Otukpa in Benue State and was taken by armed men near Odoba village along the Otukpa-Enugu Road.
Local press reports suggested he was on his way home after mediating between parishioners and the Odoba parish priest at the request of the Catholic Bishop of Otukpa.
At first his kidnappers asked for around £43,000 in ransom but then changed it to around £14,000.
His family offered £5,000 and the Benue State Governor also made an offer for information about where Fr John Adey was taken, but he was not released.
Speaking to the Nigerian paper Sunday Vanguard, his mother, Mama Martha Kate Adeyi, said: "Fr John had no problems with anybody, he served God and humanity with all his being, soul, spirit and body.
"He didn't deserve the treatment they meted to him as a servant of God. I am heartbroken, devastated, but God knows why it happened this way.
"I thank everyone who showed concern about his abduction and eventual death. I'm only pleading with government and law enforcement agencies to do justice in this matter by ensuring the arrest of the masterminds of this unfortunate incident. It is only then that Fr John will find peace and the family will also be consoled."
CSW's Chief Executive Mervyn Thomas said: "We extend our deepest condolences to the family of Father Adeyi and the Oktupa Diocese.
"It is both sad and reprehensible that clergymen, who dedicate their lives to serving for no financial gain, are being targeted for kidnapping and extortion.
"Father Adeyi is the second clergyman in central Nigeria to be found in this manner.
"On 30 March, the decomposing body of Reverend Iliya Anto was discovered in Kaduna State, nine days after he and two other clergymen had been abducted.
"Such kidnappings seem to indicate a worrying breakdown in law and order.
"While we commend the Benue State authorities for the progress made so far in tracking down culprits, we also urge the Nigerian authorities to formulate and implement a comprehensive security solution to the kidnapping phenomenon, which is increasingly affecting citizens throughout the country."
