High levels of agricultural insecticide have been found in samples taken from tainted food blamed for the deaths of 23 schoolchildren in north-eastern India.
Forty seven were taken ill after eating a free meal of rice and soya beans at a school in Bihar state on Tuesday.
Police said "very toxic" levels of the pesticide monocrotophos had been detected by scientific tests.
Vegetable oil used to prepare the food was revealed to be highly contaminated.
On Friday, police said they suspected the vegetable oil had been in a container previously used to store the pesticide.
School cook Manju Devi earlier accused school principal Meena Kumari of forcing her to use the oil, despite the cook complaining that it "smelled strongly" and looked "dodgy".
The BBC reports Ms Kumari is now wanted on suspicion of criminal negligence. She is still at large.
Nineteen of the dead children, aged between five and 12, were buried on Thursday in and around the school in the village of Dharmasati Gandaman.