School principal Meena Devi (C) covers her face as she surrenders at court in Saran district, Bihar state, July 24, 2013. STRDEL/AFP/Getty Images

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

Meena Kumari, the school principal, and husband Arjun Rai, an opposition lawmaker, were arrested and could face the death penalty if convicted over the incident which took place in July.

"Our investigation shows it was nothing less than murder," Barun Kumar Sinha, superintendent of police in Saran district, was quoted in the The Wall Street Journal as saying.

Investigating officer Raj Kaushal said 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.

Kumari and Rai denied charges that they were responsible for the children's deaths, telling police there was no deliberate act on their part.

The school's cooks told authorities that Kumari, also known as Meena Devi, 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. Most of them were "dalits," part of India's lowest caste also known as "untouchables," and belonged to very poor households.

Kumari also fled the school after the poisoning, it is alleged.

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.

Since the poisoning, schools in neighboring villages like Azad Bigha and Baluan have stopped serving the midday meal. It followed instances of students refusing to eat on the orders of their parents.

Although there have been prior 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.

The meal program, which had been suspended after the children's deaths, was reinstated in September.

Al Jazeera & The Associated Press