Ravinder Kumar, assistant director general of the Patna police, told reporters at a news conference monocrotophos, an insecticide known to be toxic to humans, was discovered in samples of oil and in a mixture of rice and vegetables, CNN reported.
The poisoning occurred at a one-room school in a village in the state of Bihar in eastern India, one of the poorest areas in the country. Witnesses said the children began vomiting soon after they finished lunch.
The school was described as a ramshackle one-room building. Like other government schools in India, it is required to provide a free lunch for pupils age 12 and younger.
The children who died or became sick were between the ages of 5 and 12.
The cook, Manju Devi, told police the headmistress, Meena Kumari, ordered her to go on with lunch preparations even thought she said the mustard oil she was using smelled bad. Devi was hospitalized while police were searching for Kumari to question her.
Bihari officials announced Friday a commission has been established to review procedures to ensure school food is safe.