NEW YORK—Since leaving his 1-year-old twins in his broiling car while he was at work Friday, killing them, Juan Rodriguez has been in a state of disbelief, struggling to understand how he could have forgotten to drop them off at their day care.

Out on bail on manslaughter charges and wracked with grief, he told a close friend that he believed he had left the children at their day care provider, even though he had not. “He couldn’t explain it,” the friend, Alfredo Angueira, said. “In his mind he dropped them off.”

Then Sunday, Rodriguez called David Diamond, a professor of psychology in Florida who studies why otherwise loving parents forget their children in cars. Rodriguez could not understand his own memory lapse, Diamond said.

“He thought he was the only person who had ever done this,” Diamond said in an interview Monday.

Diamond said he told Rodriguez that hundreds of other parents have also left their children in hot cars, with similarly tragic results. It has happened to doctors, accountants, teachers.

Since 1998, about 440 children across the United States have died of heatstroke after being forgotten in cars, generally not because of a lack of love, Diamond said, but because of how human memory functions.

“I think this has helped him in his time of grieving,” he said, “to understand how it’s possible he could do this.”

Rodriguez has not spoken publicly, but the comments by Angueira and Diamond offered the first insights into how he is grappling with the devastating reality of having left his children to die.

Rodriguez, who lives in Rockland County, N.Y., told police he assumed he had dropped the babies off. He said he arrived at work in the Bronx at 8 a.m., put in a full shift counselling people at a veterans’ hospital and had already started driving home at 4 p.m. when he discovered the twins still strapped in their rear-facing car seats, no longer breathing, police said.

He got out of the car and screamed, alarming bystanders. “I blanked out,” he told police. “I killed my babies!”

Diamond explained that about half the children who had been mistakenly left behind in cars since 1998 died in very similar circumstances to those of Luna and Phoenix, Rodriguez’s children. A parent or caregiver had meant to drop the children off at day care or preschool but forgot, leaving them in the car.

July is the most common month for children to die of heatstroke in cars, according to data on hot car deaths complied by Jan Null, a meteorologist at San Jose State University. And Thursdays and Fridays are the most common days for such deaths.

It was a Friday when Rodriguez, a 22-year veteran of the National Guard, left his children in the car while he went to his job as a social worker at the James J. Peters VA Medical Center.

“It fits the same patterns that we have seen in a lot of these forgotten-child cases,” said Null, who founded noheatstroke.org to try to save children’s lives. “It was a good parent, who for some reason, went on to work, and didn’t remember he hadn’t dropped off his children.”

Creating a false memory that the children were safely dropped off is common among parents in these cases, researchers have found. Some parents have even returned to the day care to pick up their children, only to find them dead in the back seat, Diamond said.

The problem has worsened since the mid-1990s, researchers said, when safety concerns about air bags and accidents led experts to recommend car seats be placed in the back seat and often to be rear-facing, leaving children out of view.

Such memory lapses, Diamond said, have to do with how the brain functions. When people drive a familiar route, they tend to go on autopilot, a habitual state that allows them to multitask and do things like carry on a conversation at the same time.

But being in that state also suppresses the higher-order part of the consciousness that enables people to remember they had made a plan.

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People forget children in cars, he said, for the same reason people might drive straight home instead of stopping at the grocery store, even though that had been their original intention. It often takes a cue to jar drivers back into full consciousness and remember what they planned to do. Stress and sleep deprivation can make these memory lapses more common, he said.

Pediatric death in a hot car can happen fast. On an 86-degree day, like it was Friday, the temperature in the car will rise to 115 degrees Fahrenheit in 20 minutes. After 30 minutes, the car temperature will reach 120 degrees, Null said. Even with outside air temperature in the 60s, temperatures inside cars can quickly hit unsafe levels for children and pets left inside because of how cars retain heat.

Phoenix and Luna were found by the medical examiner to have had a body temperature of 108 degrees when they died, which had caused their organs to shut down. On Monday, a 2-year-old boy died in a hot van that was parked outside of a day care centre in Oakland Park, Fla., becoming the 24th child to die in a hot car this year nationwide.

Most efforts to prevent these deaths — which average 38 per year nationally — centre on providing reminders for drivers to check for their children. A simple idea is for caregivers to sign a pledge to alert parents if a child is not dropped off at day care as planned.

There are also technological solutions, such as a motion detector that can discern even the slightest movement in a car when a driver leaves. The Hot Cars Act of 2019, now before Congress, would mandate the installation of technology that at a minimum would remind drivers to check the back seat.

According to Null’s research, 54 per cent of the 795 children who died of heat stroke in cars between 1998 and 2018 were forgotten by their caregivers. The rest of them had either gotten into the cars on their own and were trapped there (26 per cent) — or were knowingly left in vehicles (19 per cent).

In the end, whether parents are prosecuted for forgetting their children in a car comes down to an individual district attorney’s discretion. In Rodriguez’s case, he has been charged with two counts each of manslaughter, criminally negligent homicide and endangering the welfare of a child. His wife, Marissa A. Rodriguez, is standing by him, saying it was a horrific accident.

Angueira, 42, who said he had known Juan Rodriguez for about 20 years, described him as a responsible father who had served in Kuwait with the U.S. Army until March 2017, when he injured his leg. He then got a master’s degree in social work at the State University of New York at Albany.

Rodriguez, who grew up in Washington Heights and the Bronx, still serves in the National Guard. He has two other children — aged 12 and 16 — from a previous relationship, and was a devoted parent whose Facebook feed was littered with family photos, friends said.

He drove to Albany every other weekend to collect his older children and would sometimes lunch with his younger children at their day care, friends said. Earlier this month, he had rented a bouncy house and a cotton candy machine to throw a big party for the twins’ first birthday.

On Friday morning, Rodriguez left his house in New City, N.Y., with the twins and their 4-year-old brother, Tristan, in the car, Angueira said. He was tired and relieved the week was at its end. He took Tristan to his day care but then forgot to drop off the twins. Then he drove to the Bronx and left the car in a sunny parking lot.

Linda Ruban, a friend who has worked with Rodriguez for 10 years, said he has been unable to eat or sleep. “‘I can’t believe that I would forget this — these are my children,’” she said he had told her.