The murder of Dr Graham Staines, 58, and his sons, Philip, 10, and Timothy, eight, marked a dramatic escalation of the terror campaign against Christians which began last year after the general election brought a coalition government led by the Hindu nationalist Bharatiya Janata Party (BJP) to power.
Witnesses at the scene of Saturday's atrocity told reporters that the crowd was chanting slogans including "Bajrang Dal Zindabad!" - "Long live Bajrang Dal!" - as they pelted the Staines' vehicle with stones before setting it alight.
The Bajrang Dal is an extreme Hindu nationalist organisation linked to the BJP, which gained international attention last year when one of its leaders called for all foreign missionaries in India to be expelled. A local Bajrang Dal activist, Darah Singh, has been named by police as the suspected ringleader of the murders, and a reward has been offered for information leading to his arrest.
Dr Staines, who had lived and worked in India since 1964, had driven with his sons some 15km from his home to the village of Manoharpur, in an area predominantly populated by tribal Christians, to participate in a Christian camp. The camp was due to finish yesterday.
Dr Staines, secretary and treasurer of the Evangelical Missionary Society in the area, had been working with fellow missionaries to eradicate leprosy from the state. Since 1982 he had been director of a local leprosy hospital.
He had focused his life's work on one of the most spectacular but also most undeveloped regions of India, where a quarter of the population consists of Adivasis, "ancient inhabitants" or tribespeople.
The rugged hills, among the oldest in the world, are still densely forested, roads are primitive and the incursions of civilisation are few.
Because of the primitive conditions, Dr Staines was in the habit of bedding down in his jeep when travelling out of his normal area of operation, and he, Philip and Timothy had piled straw on the roof of the jeep to keep out the winter chill before going to sleep.
The straw had a ghastly utility which they could not have foreseen. When they woke, the car was surrounded by a frenzied mob, said by witnesses to have been 50 to 100 strong.
Repeatedly the missionary and his children tried to break out of the car, but repeatedly they were forced back in. Then the mob poured kerosene over the vehicle and set it alight. The three bodies were reportedly reduced to ashes.
Dr Staines's wife, Gladys, was informed of the deaths of her husband and children by telephone at 4am on Saturday.The couple also have a 13-year-old daughter, Aister.
Mrs Staines told reporters that her husband "did not have one enemy in the world, and that's what makes this mind-numbing deed all the more surprising".
She said she was "shocked but not angry" and told Evangelical church authorities she feared that "local RSS was involved" in the murder.
The RSS - Rashtriya Swayamsevak Sangh - to which both the Prime Minister, Atal Behari Vajpayee, and the Home Minister, L K Advani, belong, is a paramilitary Hindu nationalist organisation. On Sunday, Mr Vajpayee said he condemned the murders and that those responsible should be punished severely. Police in Orissa arrested 47 people suspected of involvement.
The grisly murders in Orissa take the persecution of India's small minority of Christians - 2.5 per cent of the population, according to the 1991 census - to a new pitch of gravity and horror.
Attacks on Christians by nationalists, many occurring in the state of Gujarat in the west of the country, havemultiplied in the past month, starting with an attack on Christmas Day. Since then more than 30 churches have been destroyed. Two more were ransacked in Surat on Friday night, allegedly in retaliation for an attack on a Hindu temple. But this is the first case of murder to be reported.
Mr Vajpayee is under increasing international pressure to take action against the extremist allies of his party who are responsible. In the past few days, the US Deputy Secretary of State, Strobe Talbott, has added his voice to those of the Foreign Secretary, Robin Cook, and other European ministers in condemning the anti-Christian violence.
However, Mr Vajpayee's party stands to benefit electorally if tribal Christians - most attacks have been in tribal areas - can be terrorised back into the Hindu nationalist camp.