BIHAR, India (CNN) -- A father holds his limp child in his arms, carrying her from the school he trusted to take care of her. A video camera focuses on his face locked in total anguish. Everyone around him is shouting. He goes to the back of an open van and struggles to keep the white blanket he's wrapped around his child's body from slipping away as he lays the body down.
This moment came in the wake of the deaths of 22 Indian children who were poisoned by school lunches they were given on Tuesday. On Thursday, police told CNN that investigators have been unable to find the headmistress of the school in order to question her.
Authorities have not named the headmistress and her husband, whom they also want to interview, local police chief Sujit Kumar said Thursday.
The students, who authorities said were between the ages of 5 and 12, started vomiting Tuesday soon after their first bite of rice and potatoes at the school in the northern state of Bihar. Some fainted.
On Thursday, 25 people remained hospitalized, including the school cook, whose accounts of the incident are under scrutiny.
Bihar state Education Minister P.K. Shahi said the children were poisoned by an insecticide that was in the food.
Shahi said he heard reports that the school's cook had questioned the quality of the oil she was supposed to use, but was overruled by the school's headmistress.
"The information which has come to me indeed suggests that the headmistress was told by the cook that medium of cooking was not proper, and she suspected the quality of the oil," Shahi said. "But the headmistress rebuked her, and chastised the children, and forced them to continue the meal."
It's unclear how the children were "forced" to continue eating.
On Thursday, the cook, Manju Devi, told Reuters on tape: "When I saw the oil it looked like it had a layer at the bottom of the jar. I thought that this is locally made oil, as often there is an accumulation of residual waste at the bottom when the oil is domestically prepared. Generally we get just about enough oil to prepare one meal, as there is no space for storage."
But in a later interview with CNN the same day, the cook said she didn't suspect anything unusual about the oil.
District magistrate Abhijit Sinha said an inquiry into the deaths is under way, CNN sister network CNN-IBN reported.
Investigators have taken seven samples of food particles at the school and have sent them for examination, Kumar told CNN, adding he expects a report back Thursday night.
Authorities have gone to the headmistress' house and found stacks of vegetables and grains, Kumar told CNN Thursday. They did not find any pesticides, he said.
"In any Indian home you will find vegetables and grains. These are all allegations," he said. "Everybody is alleging that she is the one responsible and as a professional police officer, I'll collect evidence and only then I will know."
He said the investigation is ongoing and that "if there is a basis for it," authorities will arrest the headmistress.
"But we at least have to speak with her and get her statement," he said.
Kumar told CNN that he was going to the hospital, where he hoped to speak with the ailing children and their families.
At the same time, attention is turning to government accountability over the school food program that feeds more than 100 million children, but often with different standards across the country.
Protests were held in the area near the school, according to video CNN has viewed. In one instance, protesters appear to be beating a school bus with sticks.
Regarding the varying standards applied to how the school program is administered, Reetika Khera of the Indian Institute of Technology in Delhi said, "It is just a reflection of the sort of neglect ... and these sorts of concerns in that state and states around that area."
"In the southern part of the country," she continued, "children get not only good quality food, they also get very nutritious food," she said. "But this is not the case in Bihar."
The school meal program is run by the Indian government in collaboration with state governments, Khera said.
But she said substandard school food is "a reflection of a more general problem, which is the lack of political interest in these programs and -- very importantly -- the lack of accountability."
Shahi, the Bihar state education minister, told CNN that 20 million children receive hot meals in about 73,000 elementary schools.
"We have been endeavoring to improve the quality and ... try to get good food served," he told CNN's Michael Holmes.
"However, the challenge is still there because the magnitude of this program is so huge that there are a number of challenges." He said those challenges are at least partly financial.
"Even though I would unhesitatingly admit that there are some quality issues before us, this is the first incident which has happened in the state," Shahi said. "In the past, we have received complaints regarding quality, but the incident of this nature ... has really shocked us -- shocked the entire state."
It's unclear whether the children were intentionally or accidentally poisoned.
But officials believe the poison was an organophosphorus compound, a type of chemical that the U.S. Centers for Disease Control and Prevention says is commonly used in agriculture.
It's a nerve agent related to sarin gas, which is used in chemical warfare, the U.S. Health Department says.
Exposure to a high dose can cause an irregular heartbeat, difficulty breathing, paralysis and seizures.
Violence erupted Thursday when dozens of men reportedly attacked one of the base kitchens of the Ekta Shakti Foundation -- a non-governmental organization that supplies lunches to more than 1,200 schools in the Chhapra district of Patna.
The group's vice president, Rajnikant Pathak, told CNN the foundation had already stopped supplying meals to students Wednesday after news of the deaths.
A program providing one free hot meal a day to school children has proved incredibly popular as part of India's wider effort to tackle malnutrition. Children ages 6 months to 14 years get take-home rations or are provided with hot cooked food.
The wider $22 billion-a-year welfare scheme aims to sell subsidized wheat and rice to 67% of its 1.2 billion people.
According to the Indian government's figures, nearly half of India's children suffer from malnutrition of some sort.
Since a landmark Supreme Court decision in 2001, all government schools in India have been required to provide free meals to students younger than 13.
CNN's Sumnima Udas, Harmeet Singh and Aloke Devichand reported from Bihar; Holly Yan and Ashley Fantz wrote from Atlanta. Elizabeth Joseph contributed from Hong Kong. CNN's Tim Hume and journalist Neha Sharma also contributed to this report.