Detectives are investigating claims a father wrote a letter confessing to murder before killing a man and then taking his own life in Peterborough.
Cambridgeshire Police found the body of Roy Allison, 65, of Hetley, Orton Goldhay, hanging in the grounds of Peterborough Crematorium on Sunday.
It came after the discovery of another body belonging to Duncan Bell, 36, from Winyates, Orton Goldhay. He had been stabbed in the heart.
Claims have emerged that Mr Allison sent a number of letters, including to the police and his local newspaper the Peterborough Telegraph, setting out his intentions. In it he blamed Mr Bell for his son's sudden death three months ago.
The letter claims Mr Bell gave his son, Roy Allison Jnr, drugs during his 28th birthday party. It adds that Mr Allison Snr was "furious" that Mr Bell continued to live a prosperous life after his son's death.
A spokesman for Cambridgeshire Police confirmed the force was aware of the letter which "purported" to be from Mr Allison Snr.
Detective Inspector Liz Mead, who is leading the inquiry, said: "Inquiries are continuing into the tragic set of circumstances that appear to have led to these two deaths. We remain in contact with the families of both men."
One relative of Mr Allison Snr told the Peterborough Telegraph: "Roy had it stuck in his mind that somebody had given his son drugs. He was determined to find out who gave him the drugs and kill them."
In a statement, Mr Bell's family said: "There is little that can be said that could ease all our grief now. Some people make such a difference in our lives, Duncan was one of those people.
"By simply being who he was he made the world a better place, he touched so many lives and now he's gone we all realise how lucky we were to have known him."