Jeetu alias Jitendra, a resident of Mathura, was having an illicit affair with the woman - his neighbour, they said.
On January 2, Jeetu stragulated the boy to death in Sector 96 and hid his body behind bushes, ASP Gaurav Grover said.
Last night, the police recovered the body of the boy.
The plan to kill the boy was hatched by the two, police said.
According to police, he used to accompany the boy's father to the police station to avoid any suspicion by authorities.
Yadav said Jeetu killed the boy because he had threatened to tell his father.