Since leaving his 1-year-old twins in his broiling car while he was at work on 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 on Sunday, Mr. Rodriguez called David Diamond, a professor of psychology in Florida who studies why otherwise loving parents forget their children in cars. Mr. Rodriguez could not understand his own memory lapse, Dr. Diamond said.

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

Dr. Diamond said he told Mr. 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 nationwide have died of heatstroke after being forgotten in cars, generally not because of a lack of love, Dr. 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.”

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

Mr. Rodriguez, who lives in Rockland County, N.Y., told the 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 counseling 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, the police said.

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

His wife, Marissa A. Rodriguez, is standing by him, saying it was a horrific accident.

On Sunday, she said in a statement that the deaths were “my absolute worst nightmare.”

“Though I am hurting more than I ever imagined possible, I still love my husband,” Ms. Rodriguez said. “He is a good person and great father and I know he would’ve never done anything to hurt our children intentionally.”

Dr. Diamond explained that about half of the children who had been mistakenly left behind in cars since 1998 died in very similar circumstances to those of Luna and Phoenix, Mr. 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.