Senior Superintendent of Police K Ravindra Gaud told reporters that the accused, Baburam Kashyap, got married to Neelam (19) on July 17 this year.
On August 3, Baburam called Neelam, who was at her parents' house, and said that he wanted to her to take to the 'sawan mela' at Bhauapur village.
The SSP said that Baburam picked Neelam and her sister Sangeeta (14) and took them to a sugarcane field, where he strangulated the sisters to death.
Gaud said that family members of Baburam were detained after which the accused was also arrested.
He said that on Baburam's identification skeletons of the two sisters were later recovered from the field.
Local police station in-charge Vipin Kumar Maurya said that Baburam wanted to marry his cousin sister, and to clear the way he killed his wife and sister-in-law.