A Kings Park man was found guilty of manslaughter Friday in the death of his infant son in 2011.

Christopher Foster, 32, was convicted of first-degree manslaughter and endangering the welfare of a child. He faces 8 1/3 to 25 years in prison.

His son, Jonathan Hertzler, was 43 days old on Oct. 11, 2011, the day he died. His injuries included a fractured skull and broken bones. Foster was found not guilty of second-degree murder.

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"A verdict of guilty of manslaughter is justice for a 6-week-old baby that had no chance and we gave him a voice today," Assistant District Attorney Dana Brown said after the verdict was handed down.

Foster's friends and family were visibly shaken by the verdict and did not want to comment.

Defense attorney David Besso of Bay Shore said he planned to appeal.

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"There is really no evidence to support the verdict," Besso said outside the courtroom. "I believe Mr. Foster is not guilty and we will be vindicated in the end."

Prosecutors contended Foster never wanted the child while the defense said Foster was not ready to have a child because he and Clarissa Hertzler had been dating only three months when she became pregnant. The couple broke up after Hertzler told him she was pregnant and reunited shortly after Jonathan was born, according to testimony at trial.

In closing arguments Wednesday in Riverhead, prosecutors called Foster "callous" and "indifferent to human life" because he was more worried about going to work the day the infant died.

Brown held a picture of the injuries to Jonathan's bruised skull to counter the defense's earlier argument that there was no evidence Foster killed his son.

Foster's defense lawyer countered there was no evidence he was the person who caused the injuries, and said there was another person in the household who was responsible.

Brown told jurors Foster was stoic the day police responded to his home after a frantic 911 call that his son was not breathing. Prosecutors replayed the call and Clarissa Hertzler, the baby's hysterical mother, was heard in the background while her mother talked to dispatchers. Brown reminded jurors of testimony from responding officers describing Foster as "an unemotional father."

Defense attorneys said the baby's grandmother, who suffers from schizophrenia and lived with the family, may have caused the infant's death. Prosecutor's said investigators ruled out the grandmother as a suspect early in the investigation.

During the trial, Foster's cousin, Jonathan Foster, testified the baby's grandmother told him, "Jonathan, sometimes I hear voices to kill" when he visited the apartment the day after the infant died.

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Christopher Foster remains held without bail and is scheduled for sentencing Sept. 8.