Parents of the couple, who used to live with them, informed Masuri Police Station that the deceased did not wake up despite repeated knocking on their room door, which was bolted from inside. They then peeped in through the window to witness the gruesome scene, said Senior Superintendent of Police (SSP) Ghaziabad Sudhir Kumar Singh.
According to him, a police team reached the residence in New Shatabdi Nagar and broke open the door to recover the bodies of Pradeep (41), his daughters Mansvi (8), Yashaswi (5) and Ojaswi (3).
Pradeep's wife Sangeeta (40), who was earlier a nurse in the All India Institute of Medical Sciences (AIIMS), was found breathing so she was rushed to a nearby hospital, where she succumbed to her injuries.
The parents told the police that Pradeep had recently lost his job at a private company, owing to which relations between the couple became tense. He had also started drinking.
"The crime scene suggests that Pradeep first a administered poisonous substance to his wife and children. When they started becoming unconscious, he wrapped their mouths and noses with a four-inch wide tape and hit their heads with a hammer. At last, he himself consumed heavy dose of poison and committed suicide, Singh said.
"A suicide note was also recovered in which the man stated that he suspected his wife of having an illicit affair due to which there were frequent quarrels between them. The note said tired of the fights, he killed his wife and children," said SSP Singh.
The bodies have been sent for post-mortem.
( With inputs from IANS )