According to police, the widow, who had been given a job as a constable on compassionate grounds after her husband was killed by Maoists, was accompanied by relatives as she was taking the body to Garwah, about 150 km from Ranchi, Thursday night.
The criminals stopped the vehicle near Jaldaga bridge of Latehar district, around 130 km from Ranchi, and looted the relatives who were accompanying the body.
Three of the men then allegedly gang-raped the woman constable, in the very vehicle in which the body was kept.
The constable lodged a complaint with police Friday. She also underwent a medical check-up.
Police have launched a hunt to nab the people involved in the crime.
Jharkhand has witnessed a spurt in incidents of sexual crime in recent months. In Pakur district, six minor girls were gang-raped at two places last month.