Kent County’s youngest convicted killer lost a bid to have his first-degree murder conviction overturned in the Aug. 2014 stabbing death of a nine-year-old boy in Kentwood.

Attorneys for Jamarion Lawhorn contend the lesser offense of voluntary manslaughter should have been presented to jurors. They also say an autopsy photo shown at trial was inflammatory and comments Lawhorn made to an investigator should have been suppressed.

Earlier: Attorney: Jamarion Lawhorn making strides in juvenile detention

In a 6-page unpublished ruling released Friday, May 19, the Court of Appeals disagreed. “Reversal is unwarranted,’’ justices wrote.

Lawhorn was 12 when he plunged a knife into the back of Connor Verkerke at Pinewood Village mobile home park after Verkerke fell off a slide. Prosecutors contend Lawhorn had been planning to kill someone for more than a year.

“Given that the jury found (Lawhorn) guilty of first-degree murder and rejected the necessarily included lesser offense of second-degree murder, any error in not instructing the jury on voluntary manslaughter was harmless,’’ justices wrote.

There was no evidence that Lawhorn killed Verkerke “in the heat of passion caused by adequate provocation that would have made a reasonable person lose control and commit the stabbing,’’ justices ruled.

The Appeals Court also said an autopsy photo was properly admitted at trial because it assisted the prosecution in establishing Lawhorn’s intent to kill.

Related: Connor Verkerke's grandmother publishes book about his death

Statements Lawhorn made to a detective should have been off limits, according to the appeal. Lawhorn told the detective he was a “bad kid,’’ that he was “always getting into trouble,’’ that he “wanted to die,’’ and that he wished to be “put in the electric chair or given the lethal injection.’’

Those statements were fair game, given an insanity defense presented at trial, justices said.

Lawhorn also contends the court should have entered a judgment of guilty but mentally ill. That too was shot down.

“Here, the jury found beyond a reasonable doubt that (Lawhorn) committed first-degree murder and rejected his contention that he was legally insane at the time,’’ the Appeals Court wrote. “It also did not find him guilty but mentally ill.’’

At trial, Lawhorn’s attorney argued that years of physical and psychological abuse had taken its toll. The tipping point came the morning of Aug. 4, 2014 when Lawhorn's stepfather promised him a beating for using a computer without permission.

His lawyer argued that Lawhorn’s bottled-up angst exploded in a gruesome attack on Verkerke, who was stabbed five times in the back and once in the arm with a kitchen knife Lawhorn hid beneath the playground sand.

Two of the blows entered three inches into the boy's back, puncturing Connor's right lung. One was delivered with enough force to penetrate a rib.

A Kent County jury in Sept. 2015 deliberated less than five hours before finding Lawhorn guilty of first-degree murder.

Lawhorn was given a blended sentence; he will remain at the Muskegon River Youth Home in Evart until a determination is made regarding a potential adult sentence when he turns 21.

Now 15, Lawhorn was back in Kent County Circuit Court earlier this week for a six-month review hearing. A therapist testified that Lawhorn has made significant improvements since his last review hearing in Nov. 2016.

“He definitely appears to be more motivated,’’ the therapist told Judge Paul Denenfeld.

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