Updated

Prosecutors have charged a 20-year-old suburban St. Louis woman with murdering her 13-month-old son.

St. Louis County prosecutor Bob McCulloch said Wednesday that Shelby Dasher is charged with second-degree murder in the death of her son, Tyler. She was arrested early Wednesday and is being held on $500,000 cash bond.

McCulloch says Dasher admitted to police that she repeatedly struck her son because he was crying and "wouldn't lay down, wouldn't go back to sleep." He says she told police she disposed of the body.

Earlier Wednesday, authorities had not formally named Dasher as a suspect in the toddler's death and no one has been charged with a crime.

Tyler's death is being called an apparent homicide by the St. Louis County medical examiner, Fox2Now.com reports.

While it is not known how the boy died, local police chief Tim Fitch said that whoever was responsible must be "a sick person," the St. Louis Post-Dispatch reported.

Dasher was escorted to the crime scene near the cemetery earlier Wednesday, then back to the home she lived in with Tyler. Police left with evidence including several toys.

Tyler’s body was taken to the St. Louis County Medical Examiner's office where it was positively identified. A motive for the abduction or apparent homicide is also unknown at this time.

According to the St. Louis station, Tyler Dasher was found dead near the River Des Peres on Tuesday afternoon. The body was found by people walking their dog in the woods a few feet from the walking path that runs along River Des Peres on the St. Louis County side of the river.

The search mode immediately shifted into an investigation with police looking for any evidence that could solve the homicide.

A St. Louis Area Regional A.M.B.E.R. Alert was issued when the child was reported missing.  The boy's mother says she put Tyler to bed Monday night and then overslept Tuesday morning. When she went to check on the boy just before noon he was gone.

St. Louis County Police spokesman Rick Eckhard said there did not appear to be any sign of forced entry to the home, but police were checking all door locks.

A witness told police they saw someone carrying a baby just a couple of hours before Tyler’s body was found. The person was near an elementary school and was carrying the child and a blue blanket, according to the station.

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The Associated Press contributed to this report.