A school principal and her husband have been charged with murder after 23 children died from eating pesticide-contaminated lunches in July at the school in eastern India, police said Tuesday.

The trial of Meena Kumari and her husband was expected to begin soon, said police officer Varun Kumar Sinha. They were arrested and could face the death penalty if convicted.

Indian villagers prepare to bury three children who died of food poisoning, after consuming a midday meal served in a government primary school.

Investigating police officer Raj Kaushal said the principal’s husband, opposition lawmaker Arjun Rai, stored pesticide at the school that was for use at his agricultural farm. The charge sheet filed in a court in Bihar state on Sunday said the chef cooked with it by mistake.

Both denied the charges and told police there was no deliberate act on their part.

The school’s cooks have told authorities that the principal controlled the food for the government-provided free daily lunch. One of the cooks told police investigators that the cooking oil appeared different than usual, but that the principal told her to use it anyway.

The children who died were between ages 5 and 12.

India’s midday meal plan is one of the world’s biggest school nutrition programs. State governments have the freedom to decide on menus and timings of the meals, depending on local conditions and availability of food rations. It was first introduced in the 1960s in southern India, where it was seen as an incentive for poor parents to send their children to school.

Although there have been complaints about the quality of the food served and the lack of hygiene, the incident in Bihar appeared to be unprecedented for the massive food program.