ST. JOHN'S, N.L. -- Newfoundland and Labrador's largest health board has fired three staff and launched an investigation after the unexpected death of a patient at a mental health hospital in St. John's earlier this month.

The unidentified man died at the Waterford Hospital on March 13 after staff did not carry out surveillance in a mental health forensic unit as required, Eastern Health CEO David Diamond said Thursday.

The results of a preliminary investigation have been disclosed to the patient's family. A more thorough review looking at policies and procedures at the mental health forensic unit will be completed by mid-April, Diamond said.

He said he can't reveal the specifics of what the preliminary investigation has found so far. But he said Eastern Health won't tolerate disregard for protocols and as a result, three employees have been fired.

"We absolutely regret what has happened," Diamond told a news conference.

Lawyer Bob Buckingham, who represented the patient, attended the news conference and said afterward his client died by suicide through "some form of strangulation."

Buckingham said the 39-year-old man was not properly monitored after being brought from jail to the Waterford Hospital.

The man, a father of two children, ended up behind bars essentially for texting people he was ordered to stay away from, Buckingham said.

Buckingham said he's glad Eastern Health acted quickly but it won't bring back his client.

He said he has spoken to the mother of the deceased and she is "devastated."

Diamond said the medical examiner is still investigating.