CHATTANOOGA (WRCB)-- A Smyrna, Tennessee mother, accused of trying to suffocate her four-year-old son, is charged with attempted murder.

Police say the incident happened Thursday during a court mandated test at T.C. Thompson Children's Hospital.

A witness told police 41-year-old Monica Hammers grabbed her son by the arm and shook him.

When the boy began to cry, Hammers allegedly placed a pillow over his face for about five to six seconds, and then ran into the bathroom after she noticed the witness watching.

The incident was reported to police, who later questioned and arrested Hammers.

She is charged with attempted first degree murder.

The child has been placed in protective custody during the on-going investigation.