Gurmej Singh had gone to fields on May 10 but was later found to be dead inside a school's premises, they said.
During investigations, it was found that Gurmej along with his friends identified as Sukhjinder, Jugraj and Sukhraj took drugs on May 10 night.
The three accused injected Gurmej Singh, who had already consumed a lot of drugs, with heroin, following which he died on the spot.
The accused then took Gurmej's body to a nearby school and kept it there, he said.