Mufassil SHO Tuntun Paswan said the kingpin of the gang, Dilip Rishi, was caught by suspicious villagers along with two accomplices who were taking an eight-year-old girl to Hajipur village in the district.
The two accomplices fled, but Rishi was caught.
The girl had fled from her home fearing that she would be scolded by her parents after her younger sister slipped from her lap and fell on the ground.
"Rishi confessed that he used to sell children to a woman at Dighri village in Katihar. The woman would supply the children to contractors for being sacrificed before starting big infrastructure projects like construction of bridges," said Mr Paswan.
The SHO said Rishi used to get Rs 5,000 for a child and had sold four children till now.
"Rishi was in jail for four years for kidnapping a neighbour's child. He was released recently. We are making raids to nab the others," Mr Paswan added.