Patna , 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 . Forensic scientists found monocrotophos , an organophosphorus compound used as an insecticide , `` in the samples of oil from the container , food remains on the platter and mixture of rice with vegetables in an aluminum utensil , '' Assistant Director General Ravinder Kumar told reporters in Patna . Monocrotophos , which is used for agricultural purposes , is toxic to humans . The cook , Manju Devi , was hospitalized after eating the food she prepared , doctors said . Devi told police that the headmistress did not heed her warning that the mustard oil used to prepare lunch looked and smelled bad . Instead , the headmistress insisted she continue preparing the meal , officials said . Confusion , grief and despair in India 's school poisoning village . An investigation found compromised hygiene and sanitation in the school , which was running from a single-room makeshift building . Experts have said the deaths underscore the problem of food safety in the country , and have prompted discussion on how to improve national school food programs amid news that authorities had warned months ago of safety problems with the state 's school meal program . Authorities in Bihar -- one of India 's poorest states -- announced that a committee would be formed to improve food preparation in rural schools . The Bihar students , who were ages 5 to 12 , started vomiting soon after their first bite of lunch ; some fainted , authorities said . According to the Indian government , nearly half of India 's children are malnourished . Since a Supreme Court decision in 2001 , government schools in India have been required to provide free meals to students younger than 13 . India 's school meal program : Ambitious , but far from perfect . CNN 's Harmeet Singh reported from Putna and Tom Watkins wrote it from Atlanta .
Nine-member team of officers formed to track down the school principal . Police intensify presence near her village in Bihar state . Authorities record statements from 40 witnesses , including child survivors of the July 16 food poisoning .