Story highlights Police: Trepierre Hummons called 911 and pretended to be a witness

He said a man was acting irate with a gun then gave a description of himself

Hummons killed Officer Sonny Kim, 48, a husband and father of three

(CNN) While friends were commenting on his last Facebook post Friday -- and some were reading text messages indicating his plan to commit suicide by cop -- Trepierre Hummons called 911 then waited with a gun for police to arrive, Cincinnati police said.

When they did, he shot and killed 48-year-old Officer Sonny Kim, a husband and father of three, police said.

Then he opened fire on two more officers, said Cincinnati Police Chief Jeffery Blackwell

The police, while armed, didn't know what they'd walked into. That's because when when the 21-year-old Hummons called the emergency operator, he didn't hint at his plan.

Instead he pretended to be a concerned witness who'd seen a man acting erratically with a gun, according to 911 and dispatch tapes released by police.

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