PATNA, India -- Police say samples of cooking oil and leftover food taken from an Indian school where 23 children died after eating lunch this past week were contaminated with "very toxic" levels of an agricultural pesticide.

Ravindra Kumar, the additional director general of police in the city of Patna, told reporters Saturday that forensic tests revealed that the samples contained the pesticide monocrotophos in levels that were "very toxic" for humans.

The free midday meal was served to the children Tuesday in Gandamal village in Masrakh block, 50 miles north of Patna, the Bihar state capital.

Twenty-three children between the ages of 5 and 12 died from eating the meal and many others fell ill.