A Ronkonkoma mother whose infant son was killed almost four years ago found herself on the defensive Tuesday in state Supreme Court, as she explained her drug use, why she let her schizophrenic mother care for the boy and how her views on the boy's father have changed so dramatically.

The father, Christopher Foster, 32, of Kings Park, is on trial before Justice William Condon, charged with second-degree murder in the death of Jonathan Hertzler, who died at 43 days old. His injuries included a fractured skull and numerous broken bones.

During a frequently contentious cross-examination, defense attorney David Besso of Bay Shore tried to discredit the mother, Clarissa Hertzler, who is now 8 1/2 months pregnant with her second child.

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Hertzler on Monday told jurors that Foster was constantly aggravated by the baby and handled him carelessly. But she conceded that the day after the death, she described Foster much differently to police.

"I know he wouldn't hurt him," Hertzler told homicide detectives then, adding: "He loved him so much. Every night he was trying to do the right thing . . . He's never hit anyone. He's not a violent person."

Hertzler at first told Besso she couldn't recall if she said those things, but when Besso reminded her the entire interview with detectives was recorded, she said she might have said them.

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"You might have said them, or you did?" Besso said, offering to play the video. She finally said she did say them. She also told detectives that Foster was a good father.

"He's better than I am with the baby," she acknowledged telling detectives. "I know he would never do anything to his son."

Hertzler explained, "That's what I wanted to believe."

"That's how you felt about Christopher Foster at that time," Besso said sharply, and Hertzler agreed.

Hertzler also acknowledged she took OxyContin for about five years in her teens and then took methadone for several years, through the time of Jonathan's death, to get off the addictive painkiller. She said she is now taking Subutex, another narcotic like methadone taken to treat opiate addiction.

"So you've been on drugs half your life," Besso said.

Hertzler also defended her mother, Barbara Hertzler, who lived with the couple after Jonathan was born while taking medication for schizophrenia.

"She was a wonderful mother and grandmother," she said. "She was normal, like anyone else."

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"Normal," Besso said. "Did she say she was hearing voices and wanted to kill?" he said, referring to why she was hospitalized after the baby died.

Hertzler said she didn't recall that, and never asked her mother if she killed the baby.

During further questioning by Assistant District Attorney Dana Brown, Hertzler said she knew her mother would never do that. And although she initially thought that of Foster, eventually "everything kept adding up in my head," she said.