When poisoning her 5-week-old son didn’t work, a St. Paul woman admitted she smothered the baby for five minutes — even when he cried and moved his hands up and down — until he died.

Shwe Htoo, 22, said she then strapped her newborn’s body in his carrier, put him in her car and drove to Como Park, where she crashed in an attempt to kill herself.

Emergency responders quickly determined the baby had not perished in the crash. Michael Kyaw Htoo was cold to the touch and Shwe Htoo told a police officer, “This morning — I killed my own child,” according to a second-degree murder charge prosecutors filed against her Thursday.

The criminal complaint did not provide Htoo’s motive and police said it was unclear. As Htoo tried to kill Michael and then succeeded, she also tried to commit suicide three times, the complaint said.

Two passers-by gave the baby CPR — one an off-duty EMT and the other a doctor — and both were left deeply saddened by the loss.

“It was definitely the worst day of my life and now knowing what was done to the child, that’s really upsetting,” said Adam Valine, who has been an EMT for five years and works for HealthEast. “The worst call you can get” is a child not breathing “and being off duty, having no equipment … it was a lot to handle.”

Valine lives nearby and walks his dog in the park every day but usually doesn’t take the route he was on Wednesday. Suddenly, he heard squealing, a crash and the sound of an engine revving. The car crashed about 30 feet away and Valine rushed over.

Valine asked the driver if she was OK and noted “she seemed really dazed,” he said Thursday. “She said, ‘My baby,’ or something along those lines.”

He said he ran to the back and saw a baby in a carrier, which hadn’t been secured in the car, and Valine initially thought the child had a traumatic injury from the crash. Michael, who was born Oct. 12, was “bluish and was not moving,” the complaint said.

“I had the baby in my arms, trying to check for a pulse,” said Valine, 25. He said he gave the baby CPR for five to 10 minutes and then a doctor stopped to help.

Dr. Jason Wirtz had been driving to the Como Zoo with his 2-year-old son when he noticed something out of the corner of his eye, did a U-turn and saw Valine performing CPR. Wirtz, who is an adult internal medicine infection specialist and father of two, said he could tell “the infant didn’t appear to have a chance,” but he took over CPR until paramedics arrived two minutes later.

Wirtz saw the driver had moved to the car’s back seat and was sitting next to the then-empty infant car seat.

“She wasn’t wailing or crying or freaking out,” Wirtz said Thursday. “She just seemed stunned. I asked someone if she was in shock.”

Htoo soon told an officer that at 9:30 p.m. Tuesday, she had “prepared a 60 mL mixture of baby formula, sweets, three sleeping pills, and substances for killing bedbugs,” according to the complaint. She bottle-fed it to her baby and he fell asleep. At 1 a.m. Wednesday, Htoo said, she drank another preparation of the mixture.

“Later that morning, when neither she nor the baby died from consuming the mixture, Htoo covered the baby’s mouth with both hands,” the complaint said.

Police gave Htoo a baby doll, asking her to demonstrate how she killed the baby.

“Htoo, using a blanket that had been given to her by a medic, covered the doll’s mouth and nose area while pressing down with her right hand,” the complaint said. “She said she used both hands, but not at the same time. She switched hands back and forth over the baby’s mouth and nose area for about five minutes until the baby died.”

She said it happened about 6 a.m. Wednesday in her home at Hoyt Avenue and Edgerton Street.

Htoo had used a kitchen knife to try to cut her throat before she put Michael into her Honda Accord. She drove toward Como Park, about five miles from her home, “because it’s quieter and less populated,” she reported.

Htoo crashed into a light pole on Midway Parkway, near Como Avenue, about 11 a.m. in an attempt to kill herself, the complaint said.

Htoo was taken to a hospital for evaluation. Minnesota court records show she has no criminal history.

For Wirtz, it seemed like fate that he passed by the area when he did, he said. He hit about seven green lights in a row on the way to the zoo.

“If I had any stops or my morning had gone differently, I might not have been there at that moment to perform CPR,” said Wirtz, who works at St. Paul Infectious Disease Associates.

Wirtz said he was relieved that his 5-year-old wasn’t with him because the situation would have been harder to explain to her than to his toddler. The boy was “blissfully unaware” of what was happening, sitting in his car seat, Wirtz said.

But mostly, Wirtz’s thoughts have been on the baby who died and the child’s family.

“I feel so bad,” he said.

A woman who answered the door at Htoo’s home Thursday declined to comment. A small slip of paper taped next to the door listed eight people living in the house.

The ink used to write the first seven names had been faded by the elements, but it was fresh on the last name on the sheet — Michael Kyaw Htoo.

Mara H. Gottfried can be reached at mgottfried@pioneerpress.com or 651-228-5262. Follow her at twitter.com/MaraGottfried. Elizabeth Mohr can be reached at emohr@pioneerpress.com or 651-228-5162. Follow her at twitter.com/LizMohr.