Robert Crumb, the Bethpage man on trial in the November...

Robert Crumb, the Bethpage man on trial in the November 2016 stabbing death of his wife in their home, is shown at his arraignment at the Nassau County Courthouse in Mineola on Dec. 9, 2016. Credit: Howard Schnapp

A Bethpage man showed his wife no mercy after an argument about their marriage, paralyzing her in an initial knife attack their 12-year-old son tried to stop, before fatally slitting her throat a short time later, a prosecutor told jurors Friday.

But a lawyer for janitor Robert Crumb, 45, presented a self-defense theory in which he portrayed the deceased, Maria Crumb, then 41, as the aggressor who brought a knife into the room where his client was sleeping before a struggle ensued.

Defense attorney Stephen Scaring also suggested in his closing argument at Robert Crumb’s murder trial in Nassau County Court that his client’s actions on Nov. 4, 2016, in the family’s Seitz Drive home may have been influenced by his use of prescription cough medicine.

“The law for good reason gives the defendant the presumption of innocence,” the Garden City defense lawyer told a Mineola jury. “Add up all of the things that are missing at some point in your deliberations and say ‘Can I really be convinced?’ ”

But Nassau prosecutor Michael Walsh shrugged off Scaring’s assertions, saying Robert Crumb carried out a “targeted” and “purposeful” attack and was “not crazy” at the time but “vicious.”

“Everything he did was perfectly controlled,” Walsh said of Crumb, calling the cough medicine argument “a defense of desperation,” and adding that blood evidence “conclusively shows” Maria Crumb couldn’t have attacked Robert Crumb first.

Besides second-degree murder, Crumb is accused of assault, criminal possession of a weapon, reckless endangerment and resisting arrest.

Authorities have said an early-morning 911 call from the couple’s then-12-year-old son brought police to the house, where they found Maria Crumb dead in a bedroom after Robert Crumb had fled.

Prosecutors have alleged the boy tried to come to his mother’s aid when he heard her screams and jumped on his father’s back to try to stop the initial attack, before he was thrown off. Authorities also claim Robert Crumb wounded his daughter, then 16, as she tried to grab a knife from him before he carried out a second, and deadly, stabbing attack on his wife.

The man later led police on a chase that ended with a fiery explosion in Brooklyn when he drove into gas station pumps, got out of his car and charged at a police officer, according to authorities.

Prosecutors have said the capture of the defendant, who they said stabbed himself in his wrists and neck, came after police used a stun gun on him.

On Friday, Scaring criticized prosecutors for what he called mishandling of blood and urine tests to determine whether his client had adverse effects of medication. He also pointed to expert testimony that wounds on his client’s hand were “consistent” with defensive injuries, and said prosecutors “manipulated” his client’s young son before his testimony and “his story dramatically changed.”

One of the last things jurors heard was the boy’s call to 911, when he cried and told an operator: “My dad stabbed my mom.”

When it came to mercy for Maria Crumb, Walsh then told the jury, Robert Crumb “showed her none.”

Deliberations start Monday.

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