A man the late John O'Sullivan considered an enemy is now vowing he'll do everything he can to bring O'Sullivan's alleged killer to justice.

Though Amador County District Attorney Todd Riebe prosecuted O'Sullivan in the past for alleged criminal conduct, Riebe says his office is ready to go to court against Ken Zimmerman - the man accused of gunning down the controversial developer - in order to put Zimmerman away for murder.

Regardless of the history between Amador's DA and the slain Irishman, the California Attorney General's Office has declined to take over Zimmerman's case, thus leaving Riebe and his deputies with little choice but to go after the man sheriff's detectives say ended O'Sullivan's life.

Questions about who might handle Zimmerman's prosecution emerged as early as Monday morning, Aug. 17 in the hours immediately after O'Sullivan was found shot to death on his tractor. At the crux of the situation was the fact that O'Sullivan and his wife, Krista Clem, had a federal civil rights lawsuit pending against Riebe and deputy prosecutor Melinda Aiello.

After speaking with law enforcement about the known facts in the case, Riebe contacted the Attorney General's Office on how to proceed. "It's not that I felt there was a conflict," Riebe said, "but the comfort level of the victim's family was something we had to take into consideration."

Indeed, Clem told the Ledger Dispatch two days after her husband's death that she wasn't comfortable with Riebe and his staff handling Zimmerman's prosecution, mainly because in 2006 Riebe charged O'Sullivan with having killed a horse through neglect and starvation. O'Sullivan pleaded no contest to the charge, although he publicly denied that he'd mistreated any of his horses. The federal lawsuit O'Sullivan filed against Riebe stemmed from circumstances around the alleged horse neglect.

According to Riebe, officials from the Attorney General's Office didn't think his past involvement with O'Sullivan met the criteria for recusing himself in favor of the Attorney General's Office taking over Zimmerman's prosecution. "Their reasoning has to do with section 1424 of the California Penal Code," Riebe observed, "which states that a motion for recusal can only be granted if there's a conflict that renders it unlikely that the defendant would receive a fair trial. Basically, there's a clear standard that says it's only the defendant, not the victim, that's entitled to ask for a DA to recuse himself."

But the defendant, Zimmerman, is doing just that. At a pre-hearing on Wednesday, Zimmerman's attorney, Public Defender Richard Cotta, filed a motion to recuse the Amador County District Attorney's Office from prosecuting Zimmerman's case. Superior Court Judge David Richmond informed Cotta and Zimmerman that the motion hadn't been adequately filed with Riebe's office or the Attorney General's Office. Zimmerman waived time for speedy trial in order to allow Cotta the chance to refile the motion.

Michael Canzoneri, a representative from the Attorney General's Office, was also present at the pre-hearing. He informed Richmond that Clem wanted to have attorneys of her own file a motion to have the DA's office removed under rights conferred to victims and their family members under the new Marsy's Law. Such a motion to remove a district attorney has never been attempted before in California since Marsy's Law was passed. Richmond told the court he could not "operate on supposition" and would wait to comment until such a motion was filed.

Clem confirmed to the Ledger Dispatch that unidentified attorneys were working on filing the motion.

Riebe said that his office was a champion of Marsy's Law and had been one of the first to observe many of its elements before the law was passed. However, Riebe did not think there was any legal precedent for using Marsy's Law in the way Clem was suggesting.

Knowing Clem's feelings on the case, Riebe said he and Aiello would not be the ones arguing the Zimmerman case in court. Instead, he's assigned Deputy DA Joe Gasparetti, who has successfully prosecuted homicide cases in other counties. Gasparetti will be assisted by Deputy DA Steve Hermanson.

Three weeks into defending Zimmerman, Cotta said his client feels he's "committed no crime." Cotta also told the Ledger Dispatch on Monday that it was too soon to discuss elements of the defense. "It's still relatively early in the proceedings for a homicide case," Cotta said. "We're still evaluating the case."