The teenager's body was found in a metal trunk of the house, Police Commissioner Ludhina, Ishwar Singh, said.
Prima facie it appears that Sachin was hit in the head with a rod which led to his death, he said.
Chottu, who is a domestic help in the house opposite Sachin's residence, has been arrested, the police official said.
Sachin was kidnapped from his residence on May 4, and all the calls made by her mother on his mobile police went unanswered, he said.
During interrogation, Chottu said that he was harbouring a grudge against Sachin who had some time ago reprimanded him on some pretext, police said.