Killer mom Susan Smith’s ex-husband isn’t the only one standing in the way of her potential release — her trial’s lead prosecutor is also battling to keep her locked up for killing her two young sons back in ’94.

Tommy Pope, the former solicitor for South Carolina’s 16th Judicial Circuit, tells TMZ he’s joining forces with the current solicitor, Kevin Brackett, to keep Susan behind bars at S.C.’s Leath Correctional Institution for the rest of her life … saying he’ll do anything to ensure she doesn’t get out of prison. Smith has her first parole hearing set for Nov. 4.

Pope says actions have consequences … and while mental health issues can be a factor in cases of taking someone’s life, he thinks Susan’s decision to drown her young kids just to stay with a man who didn’t want children was an extreme example of selfishness.

He adds he’s pushing to keep Susan locked up for life, which he firmly believes is what the jury wanted in the first place.

Pope says, under South Carolina law, the trial judge couldn’t let the jury know Susan would be eligible for parole when they decided her fate … so he thinks when they gave her life in prison, they wanted life without parole.

He’s convinced the jury opted for life so Susan would spend the rest of her days reflecting on what she did to her kids. She was convicted of strapping her two young sons into her car and driving it into a lake, watching them drown, then telling police she had been carjacked, hindering the investigation for more than a week.