Prayagraj: An 80-year-old woman and her grandson, 40, were found dead in their village home near Phulpur town in the district on Tuesday, police said.
The police suspected that Lalita Devi and her grandson Arvind Maurya of Dhokri village died of consuming poison.
Senior Superintendent of Police Ajay Kumar said the man appears to have served some poisonous food to his grandmother before consuming it himself.
A nine-page suicide note was recovered from the spot in which Maurya held seven people, including his wife, responsible for his actions, the SSP said.
Initial investigation has revealed that Maurya's wife was having an affair with someone which was the reason of the dispute in the family, Mr Kumar said.
There were no injury marks on Lalita Devi's body and police suspected that she was given the poison first, he said.
The bodies have been sent for the post-mortem and a detailed probe is on.
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