A Marrero man was sentenced Monday to life in prison for murdering his boss at their workplace in Kenner.

John Spears, 52, was convicted last month of the second-degree murder of Anthony Tardo, 49, on Dec. 4, 2015. Judge June Berry Darensburg of the 24th Judicial District Court handed down the sentence.

Tardo was the supervisor at Houston Marine Training Services in the 2500 block of Williams Boulevard. Spears was an instructor.

Tardo was seated at his desk in his office when Spears appeared in the doorway and reportedly shouted an obscenity before he shot Tardo once in the chest.

Tardo died within a minute, according to trial testimony.

Spears then told co-workers to call 911, walked to the parking lot, unloaded his .40-caliber pistol and waited for Kenner police to arrive.

Spears pleaded not-guilty by reason of insanity, claiming mental illness and a related blackout prevented him from knowing right from wrong. But a jury convicted him June 15 after less than one-and-a-half hours of deliberations.

Tardo’s family used an impact testimony letter to describe him as a “generous, most caring person” with a “contagious laugh.” Through his “cowardly” act, Spears robbed Tardo’s wife, their three children and his extended family of a life with him, his family said.

Assistant District Attorneys Joshua Vanderhooft and Rhonda Goode-Douglas prosecuted the case.