WASHINGTON — The story was chilling and heartbreaking: A 3-year-old boy was found dead in a Southern Maryland park, his mother pushing him on the swing.

More than a month after Ji’Aire Donnell Lee’s death, the Charles County Sheriff’s Office revealed more terrible details: Ji’Aire was alive when his mother put him on the swing. He stayed on it for almost two days.

A medical examiner’s office has ruled that Ji’Aire’s death was a homicide, and the sheriff’s office said Tuesday that he died of hypothermia and dehydration during his long time on the swing. The autopsy report will be sent to the county state’s attorney’s office, which will decide whether to file charges against Ji’Aire’s mother, Romechia Simms.

Kristen Ayers, of the state’s attorney’s office, said that because prosecutors had not received the autopsy report, they cannot say whether they will file charges.

Ji’Aire was dead when police found his mother pushing him in Wills Memorial Park the morning of May 22. At the time, police were unsure when and how he died.

On Tuesday, the sheriff’s office said their investigation revealed that Simms, 24, arrived at the park in La Plata, Maryland, with her son about 11:15 a.m. May 20.

Simms, who had previously experienced a mental breakdown, stayed in the park for nearly 44 hours, pushing Ji’Aire on the swing. Early on the morning on May 22, someone who had spotted the pair at the park the day before called police to say that it was unusual that they were still there.

At 6:55 a.m., after a night during which the temperature fell to 51 degrees, police found the dead child and his mother in the park.

The police account differs from the timeline previously offered to The Washington Post by Simms’s mother, Vontasha Simms, who was living with her daughter and grandson at a motel in La Plata.

Vontasha said that Ji’Aire, a chubby-cheeked preschooler nicknamed “Sumo,” had gone to the Dollar Store and Burger King with his mother on May 21 before leaving for the park that evening.

When they didn’t return, Vontasha said she grew worried and at 12:30 a.m. May 22 called her daughter. Romechia assured her mother that they were on their way home.

Diane Richardson, a spokeswoman for the sheriff’s office, said that Vontasha’s account was incorrect and that the mother and son spent two nights in the park.

“It’s definitely Wednesday — that we know for a fact,” Richardson said. “There were witnesses there. There’s no indication that she left.”

Vontasha could not be reached to comment Tuesday. Last month, she said that her daughter suffers from depression and bipolar disorder. Romechia was hospitalized after her son was found dead but released in time for his funeral.

Romechia had been hospitalized twice before her son’s death for erratic behavior. In an interview last month, Ji’Aire’s father, James “Donnell” Lee, said she thought someone was trying to kill him in February. Not long after that, she jumped out of a moving cab with their son in tow.

Lee, who could not be reached to comment Tuesday, said he found his ex-girlfriend and child on the side of Branch Avenue after midnight. “He was walking with no socks, jacket open, in his pajamas. She left her diaper bag two blocks away,” Lee said.

Just weeks before Ji’Aire was found dead, Lee, 29, petitioned for custody of him in D.C. Superior Court, writing that he was “concerned for my child’s safety and well being.” In her written response, Romechia acknowledged that she had had a breakdown but said that she had recovered. “I am now in a much better productive space,” she wrote in April, adding, “I have done everything in my power since moving from D.C. to ensure that my son has the best life that he can have.”

On May 11, Lee and the boy’s mother appeared before D.C. Superior Court Judge Peter Krauthamer.

According to a transcript of the hearing, Lee did not reiterate his fears about his son’s safety. The judge asked, “So is there a reason why you two shouldn’t share this child? Is someone unfit here?” Lee responded, “There’s no one unfit.”

Simms received custody on weekdays and Lee on weekends. Eleven days later, Ji’Aire was dead.