The BJP says the murdered teacher, 35-year-old Bandhu Prakash Pal, was an RSS member.

The murder of a schoolteacher, his pregnant wife and six-year-old son in Bengal's Murshidabad, which has taken a political turn in the state, drew an impassioned tweet from filmmaker Aparna Sen this morning. "Shame on us," she said in the post addressed to "Madam CM" or Chief Minister Mamata Banerjee.

Aparna Sen, along with other celebrities who wrote an open letter recently to Prime Minister Narendra Modi on mob killings, has been accused by critics, including BJP supporters, of "selective outrage".

"Pregnant wife and child of RSS man slaughtered in our own West Bengal! Whatever the reason for such a gruesome act, shame on us! Madam CM! Please ensure the perpetrators are brought to justice! Irrespective of political inclinations, all citizens of WB are your responsibility. You are CM to all," Ms Sen tweeted.

Pregnant wife & child of RSS man slaughtered in our own WB! Whatever the reason for such a gruesome act, shame on us! Madam CM! Pls ensure the perpetrators are brought to justice! Irrespective of political inclinations, all citizens of WB are ur responsibility. U are CM to all! — Aparna Sen (@senaparna) October 11, 2019

A video of the Murshidabad bodies, soaked in blood and hacked with a sharp weapon, has been in circulation on social media since yesterday with leaders of the BJP prodding "liberals" to react and question the state's Trinamool government.

The BJP says the murdered teacher, 35-year-old Bandhu Prakash Pal, was a member of the Rashtriya Swayamsevak Sangh (RSS), the ruling party's ideological mentor.

Pal, his wife Beauty, 30, and young son Arya were found in different parts of their home in Jiaganj, about 210 km from Kolkata, on Tuesday, the day Vijayadashami and Dussehra were being celebrated.

That afternoon, the milkman arrived at their home and raised an alarm when no one opened the door. Locals at a Durga Puja pandal nearby broke down the door, stumbled on the bodies and saw a man run away.

The police are investigating several possibilities including a marital dispute. The family had moved to the area 18 months ago.

BJP spokesperson Sambit Patra was among those who tweeted the video and wrote: "This has shaken my conscience ...a RSS worker Bandhu Prakash Pal, his eight months pregnant wife and his kid were brutally slaughtered in West Bengal's Murshidabad Not a word by the liberals Not a letter by 59 liberals to Mamata Nauseating Selectivism!"

Escalating politics over the horrific crime, Bengal Governor Jagdeep Dhankar also commented last evening, saying there must be no cover up in the investigation into the case and it "cannot be brushed under the carpet". He also expressed dismay over the "silence" of the Mamata Banerjee government.

The Trinamool retorted that the governor is "crossing constitutional Laxman Rekhas" and suggested he keep an eye on crimes in Tripura, Bihar and Uttar Pradesh instead.