By Harmeet Shah Singh and Tom Watkins, CNN

Partna, India (CNN) - A week after an Indian school served toxic food to students, leaving 23 dead, its headmistress remains missing along with her husband, police said Tuesday. A nine-member team of officers has been formed to investigate and track down the principal, Meena Kumari, police superintendent Sujeet Kumar said.

Police presence is heavy in the village in Bihar state, especially around the principal's home.

Authorities have recorded statements from 40 witnesses, including child survivors of the July 16 food poisoning, Kumar said.

Residents went on a rampage a day after the toxic meals were served in the local government school, torching at least four police cars.

In acts of protest, parents of at least three children have buried their kids near the school - one right in front of the building, according to officials.

Police will ensure the headmistress' safety when she resurfaces or is taken into custody for questioning, authorities said.

Pesticides have been found in the food and oil used in the school lunch that sickened 25 others on July 16 in northern India's Bihar state, police said.

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