The man has been identified as 30-year-old Harish Chander, a native of Motihari district of Bihar, they said.
"Police had yesterday arrested Chander from Bihar after conducting raids at several places there. He has confessed his involvement in the murder of his brother-in-law Jairam," a senior police officer said.
According to police, Chander was suffering from some disease and undergoing treatment in Delhi.
On June 19, he along with Jairam was watching television at a high volume at his in-laws' house.
Police said he was also having grudge with his in-law's as his father-in-law had borrowed Rs 30,000 from him, but had not return the money.