TORONTO -- Prison guards say management directives against entering the cell of a teen inmate as long as she appeared to be breathing left them shocked and confused.

Travis McDonald told the inquest into Ashley Smith's death that a regional trainer told guards they were going into her segregation cell too often.

Smith strangled herself in 2007 at the Grand Valley Institution in Kitchener, Ontario.

The inquest has heard the 19-year-old frequently tied ligatures around her neck, often turning blue or purple in the process.

McDonald told the hearing yesterday that Smith even threatened to kill herself on his watch, something that left him feeling stressed and helpless.

The prison supervisor fought back tears as he testified at his distress at learning Smith had succeeded in choking herself to death.

McDonald and three front-line officers were charged with criminal negligence causing Smith's death and fired.

The charges were dropped after the Crown discovered Correctional Service Canada failed to disclose critical material about the orders the accused were given.