Story highlights Authorities had previously criticized food safety problems in the state's schools

Investigators are searching for the headmistress and her husband for questioning

Statements from the cook about the cooking oil seem contradictory

Authorities believe the poison is a sarin-like nerve gas used in agriculture

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 as he lays the body down.

The mother of a 5-year-old repeatedly calls her daughter's name.

Why aren't you coming back, she pleads.

"Why isn't anyone bringing Dipu back?!"

These moments came in the wake of the deaths of 23 Indian children who were poisoned by school lunches they were given Tuesday, authorities say.

The students, who authorities said were between the ages of 5 and 12, started vomiting soon after their first bite of rice and potatoes at their government primary school in the northern state of Bihar. Some fainted.

Photos: Deadly school lunch in India Photos: Deadly school lunch in India Deadly school lunch in India – A woman rests with her child at a ward housing the poisoned schoolchildren at the Patna Medical College and Hospital, in the eastern Indian state of Bihar, Wednesday, July 17. At least 22 schoolchildren died in northeastern India after eating free school lunches that contained an insecticide commonly used in agriculture. Officials are investigating whether the poisoning was accidental or deliberate. Hide Caption 1 of 6 Photos: Deadly school lunch in India Deadly school lunch in India – Books, papers and dishes are seen scattered on the floor after the incident. Hide Caption 2 of 6 Photos: Deadly school lunch in India Deadly school lunch in India – An Indian man mourns as he holds his dead daughter inside an ambulance, outside a hospital in Patna. Hide Caption 3 of 6 Photos: Deadly school lunch in India Deadly school lunch in India – The deaths triggered violent protests in Chhapra, the headquarters of Saran district. Hide Caption 4 of 6 Photos: Deadly school lunch in India Deadly school lunch in India – A grief stricken mother is consoled after the death of her son. Hide Caption 5 of 6 Photos: Deadly school lunch in India Deadly school lunch in India – Villagers gather for a funeral for children who died from the poison. Hide Caption 6 of 6

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Earlier, authorities had said 22 children had died, but on Thursday district magistrate Abhijit Sinha explained that one deceased boy had not been counted in the initial death toll because his father had taken his body without handing it over for autopsy.

Grief and anger so permeate this poverty-stricken community that parents of at least three children have buried their lost ones near the school -- one right in front of the building, according to CNN journalists who saw the burial mounds. Sinha told CNN that the burials were acts of protest.

Demonstrations have popped up around the area as people seek answers about how this tragedy could have happened. One video segment showed men apparently attacking a school bus with sticks. Others gathered and held signs.

Students at nearby schools refused to eat.

"I am scared now. ... There is fear in our hearts," one child told CNN sister network CNN-IBN.

Meanwhile, a top federal official said authorities had warned of safety problems with the state's school meal program months ago.

And 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.

Was it the oil?

On Thursday, 25 people remained hospitalized. Cameras captured children lying in an open space on cots; one writhed and sobbed while another stayed still, staring with glassy eyes.

The school cook, Manju Devi, is also hospitalized. The cook's 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 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 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.

Report expected Thursday night

Sinha, the district magistrate, said an inquiry into the deaths is under way, CNN sister network CNN-IBN reported.

Investigators have taken seven samples of food 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.

Government standards

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.

Investigators had previously flagged food safety issues at schools in Bihar state, noting in a report that "most schools served often average quality of food items in unhygienic condition."

The food, according to an April report from India's Ministry of Human Resource Development, "was kept in open and dirty ground."

"We had alerted the Bihar government quite a few months back about shortcomings in its food storage. We had expected that the Bihar government would have acted on the recommendations," Human Resources Development Minister Pallam Raju told CNN-IBN. "It is a failure in the system that the rectification has not been done, and I certainly hope that accountability will be called for."

"It is just a reflection of the sort of neglect ... and these sorts of concerns in that state and states around that area," said Reetika Khera of the Indian Institute of Technology in Delhi.

"In the southern part of the country, 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."

Education official: We're trying to improve

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."

What was the poison?

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.

Free meals to tackle malnutrition

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.