A teenage girl in Colorado is facing a first-degree murder charge after confessing to shoving a small rock down her newborn baby’s throat, the Denver Police Department said.

According to the Denver Medical Examiner's Office, the infant was killed shortly after birth on Sept. 8, KDVR reported. It was pronounced dead at Children's Hospital Colorado in Aurora. An autopsy revealed the cause of death was suffocation.

The mother was identified as Alaya Dotson, 16, according to the Denver District Attorney's Office. She will be tried as an adult, the district attorney's office said.

Dotson told police she didn’t know she was pregnant, according to court papers.

Police said Dotson admitted to picking up a rock and pushing it down the baby’s throat, KDVR reported. Police said Dotson admitted her role in the baby’s death after being read her Miranda rights.

She has a preliminary court hearing scheduled for Jan. 12.