New Delhi (CNN) -- The headmistress of the Indian school that authorities say served toxic lunches, killing 23 students, was arrested Wednesday, police said.
Meena Kumari, 36, was taken into custody on her way to a court where she had gone to surrender herself, police Superintendent Sujeet Kumar told CNN. She will be questioned Wednesday and taken before the court Thursday, he said.
Authorities had been working to track down Kumari, who had been at large since the July 16 incident.
The whereabouts of her husband, who is not named as an accused person in the case, are still not known, Kumar added. Police want to question him in connection with the case.
Forensic scientists found monocrotophos, an organophosphorus compound used as an insecticide, "in the samples of oil from the container, food remains on the platter and mixture of rice with vegetables in an aluminum utensil," Assistant Director General Ravinder Kumar told reporters in Patna.
Monocrotophos, which is used for agricultural purposes, is toxic to humans.
Bihar's chief minister, Nitish Kumar, vowed that police would investigate the poisoning incident from all possible angles.
"It does not appear to be mere coincidence or negligence," he told reporters after Kumari's arrest. "Police investigation will reveal everything."
The chief minister said forensic tests showed that pesticide levels in the food concerned were too high.
"The main accused (principal Kumari) is now under arrest, and every aspect of the case will be investigated," he said.
The child survivors of the incident were hospitalized in stable condition, and Nitish Kumar said he had advised that they be kept under medical care longer.
A cook, Manju Devi, was also hospitalized after eating the food she prepared, doctors said.
Devi told police that the headmistress did not heed her warning that the mustard oil used to prepare lunch looked and smelled bad. Instead, the headmistress insisted she continue preparing the meal, officials said.
Authorities previously said police would ensure the headmistress' safety when she was found.
The children's deaths prompted angry demonstrations from residents.
In acts of protest, parents of at least three victims have buried their children near the government-run school -- one right in front of the building, according to officials.