A St. Paul woman covered her month-old son’s mouth with a blanket Wednesday morning and then pressed a hand into his face, alternating hands for five minutes until the child stopped crying and moving, according to a murder charge filed Thursday.

Shwe Htoo smothered her son, Michael Kyaw Htoo, after the poisoned formula she bottle-fed the infant Tuesday night failed to kill him, authorities allege.

Htoo, 22, was charged in Ramsey County District Court with second-degree murder with intent for killing her son, who was born Oct. 12.

“This morning — I killed my own child,” Htoo allegedly told police.

Authorities don’t know what prompted Htoo to harm her child, said police spokesman Steve Linders. The criminal complaint filed against her did not provide any insight on the motive.

A relative at the family’s home said Thursday that they did not wish to comment. At the bottom of a list of names posted above the mailbox was that of the home’s newest member handwritten in black ink: Michael Kyaw Htoo.

Authorities arrested Htoo after she attempted suicide by driving a car into a light pole in Como Regional Park about 11 a.m. Wednesday. Her son, already dead, was strapped into a carrier in the vehicle’s back seat.

“Medics said Michael Htoo was cold to the touch, had dilated and fixed pupils, and had signs of rigor mortis present,” the murder charge said.

Authorities believe Htoo killed her son about 6 that morning.

According to the complaint: Witnesses heard the car crash in Como Regional Park and came upon the vehicle to find Htoo “in shock” and her child “bluish” and not moving.

One witness, an emergency medical technician, performed CPR on Michael until a doctor arrived and took over.

Htoo told an officer at the scene that she had killed her son. She was arrested and allegedly told police that she poisoned her son about 9:30 p.m. Tuesday with a mixture of baby formula, sweets, three sleeping pills and a pesticide for killing bedbugs.

Htoo fed the mixture to the boy in their bedroom. About 1 a.m. Wednesday, she drank another preparation of the same mixture.

But when mother and child both awoke Wednesday, Htoo decided to smother the child, authorities allege. Using a doll and a blanket, she later demonstrated to police how she smothered her son, who cried and waved his arms as he suffocated.

Htoo told police she used a kitchen knife to slash her neck, and drove to Como Park to commit suicide because it was quiet and less populated, the complaint said. She did not complain of injuries related to the crash, and was taken to Regions Hospital for an evaluation.

It’s unclear what Htoo did in the hours between smothering her child and crashing the car.

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