LOS ANGELES - Orange County District Attorney Tony Rackauckas had a conflict in calling for a grand jury probe into the 1988 slayings of auto-racing legend Mickey Thompson and his wife because the prosecutor once represented a Thompson relative in probate matters, a defense attorney alleged Friday in court documents.

In a motion demanding that Rackauckas remove himself from the murder investigation, Irvine defense attorney Jeffrey Benice outlined a 13-year relationship between Orange County's chief prosecutor and Thompson's sister, Colleen Campbell. Benice said Campbell repeatedly has accused his client, Michael Goodwin, of orchestrating the killing of Thompson and his wife, Trudy, on March 16, 1988, at the couple's home in the affluent Los Angeles County community of Bradbury. A hearing on Benice's motion is set for Aug. 20 in Orange County Superior Court.

"Rackauckas investigated the Thompson deaths and actually litigated whether Mickey or Trudy Thompson died first, on behalf of the Thompson family and Campbell," Benice said after filing his motion. "How can there be a fair investigation when there is such bias?" Benice asked.

District attorney spokeswoman Tori Richards denied any conflict. Rackauckas has not named Goodwin as a suspect in Thompson killings, she said.

Authorities have said two men on bicycles fatally shot Thompson and his wife. At the time, Goodwin had just lost $514,000 to Thompson in a civil dispute, and Los Angeles County sheriff's deputies suspected Goodwin had hired the killers. After failing for years to nail the case, Los Angeles sheriff's deputies looked for help from their colleagues in Orange County, where Goodwin lives and where they alleged some clues pointed.

Rackauckas' relationship with Campbell began eight months after the murders, Benice alleged. Rackauckas was an attorney then with the Law Offices of Richard S. Rockwell in Tustin, which represented the Thompson family.

In probate matters, Rackauckas filed declarations of witness-statements about the killings and documents concerning the Thompsons' autopsies, according to Benice's court papers. Rackauckas also represented Campbell in matters involving her brother's estate, Benice said. "Rackauckas is biased and will engage in a myriad of wrongful acts [that violate] Goodwin's constitutional rights [in order] to secure an indictment," Benice said in his motion.

Citing an appellate decision from 1997, Benice said the mere "appearance of conflict" between the district attorney and a defendant is enough to question the integrity of the justice system. Lewis v. Superior Court, 53 Cal.App.4th 1277 (1997). An appellate court ruled last month that Goodwin cannot be forced to participate in a lineup because he has not been arrested or indicted.

During Benice's news conference Friday, the district attorney's office subpoenaed him to appear before the grand jury at 9 a.m. Tuesday. Laughing, Benice said he will appear but is barred by the attorney-client privilege from revealing any information to the panelists.