NEW DELHI — Nine days after she disappeared, the principal of a school in eastern India where 23 children died after eating a lunch tainted with pesticide was arrested Wednesday by the police.

The principal, Meena Kumari, had been on her way to surrender before a judge in Chapra when she was detained by the police, the district police chief, Sujeet Kumar, said by telephone.

Ms. Kumari was among the most wanted people in India after she fled her school in the village of Dharmasati Gandawa in Bihar’s Saran district when the children in her school started vomiting soon after eating a free lunch. Forensic tests have confirmed that the cooking oil used to prepare the meal of rice, beans, potato curry and soy balls was contaminated with pesticide. Ms. Kumari bought the cooking oil from a store owned by her husband, who might have kept the cooking oil in a container once filled with pesticide, the police said.

Since the only other adult at the school was the school’s cook, who also fell deathly ill, Ms. Kumari’s departure meant that the ailing children were left to fend for themselves, according to villagers and state officials. Some staggered home to die in the arms of their parents.