A "mentally unstable" man allegedly killed his parents and sister with an axe in Rajasthan's Nagaur district while they were asleep, police said.

The police said that the accused, 20, remained in the house with the dead throughout the night after committing the crime on Saturday.

On Sunday morning, he "nonchalantly" went to the police station and reported the triple homicide.

"Dilip Singh (45), a resident of Padukalan town, his wife Rajesh Kanwar (40) and daughter Priyanka (15) were attacked and killed by Mohit (with an axe on Saturday night," Padukalan SHO Manvendra Singh said on Sunday.

He said after a preliminary investigation it is suspected that due to a family feud, the couple's son Mohit carried out the murders.

"Prima facie, it appears the youth is mentally unstable. However, police are still quizzing him to ascertain the actual cause. He surrendered before the police. His mobile phone showed that he seemed to have searched on the internet about committing suicide on the internet. All possible angles are being investigated," Nagaur SP Narayan Togas said.

The police said that the bodies have been kept in the hospital mortuary for post-mortem. 

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)