A criminal defense lawyer who, as an assistant Hudson County prosecutor, had a supervisory role in running a sex crimes unit is ethically barred from representing a suspect snared nine months after the lawyer left office, an appeals court says.

Though Donald Gardner, now of North Bergen’s Camacho Gardner, had no direct role in the identification or arrest of his eventual client, Elmo Rivadeneira, he had “substantial responsibility” for the investigation that led to the charges, the court held Tuesday in State v. Rivadeneira, A-1033-09.

Gardner had general power to review investigatory files and reports; to participate in discussions about ongoing matters; to assign cases to assistant prosecutors and investigators; and to effect the transfer of investigators out of his unit.

All of that made him subject to Rule of Professional Conduct 1.11(a)(1) and (2), forbidding a former government lawyer from appearing in a matter “in which the lawyer participated personally and substantially as a public officer or employee” or “for which the lawyer had substantial responsibility as a public officer or employee,” the court said.

The ruling, though unreported, is notable for begging the question: for how long must a prosecutor be out of office for the RPC’s bar to erode?

Until his retirement in January 2006, Gardner was attached to Hudson County’s Sexual Assault Victim’s Assistance (SAVA) Unit, which was involved in investigating a series of kidnappings and rapes in northern New Jersey and New York. Nine months after Gardner left, Rivadeneira was identified as a suspect and was charged in a 41-count indictment.

When Gardner entered his appearance for Rivadeneira, Hudson County prosecutors moved to disqualify him, claiming he was intimately involved in a supervisory capacity with the investigation that led to the arrest.

At the motion hearing, Gardner admitted he was a supervisor but claimed he had been detached from the investigation. He said he had been too preoccupied with other office projects and had surrendered many aspects of his supervisory role in anticipation of retiring and going into private practice with Milagros Camacho, a former SAVA Unit colleague. Gardner acknowledged he had access to “chief sheets” — reports prepared for the chief of investigations — but said he read them sporadically.

But Gardner’s testimony conflicted with that of a SAVA investigator who said Gardner was intimately involved in meetings during which the serial rape investigation was discussed.

Superior Court Judge Camille Kenny sided with the state, finding that Gardner had “substantial supervisory authority” for the investigation that led to Rivadeneira’s charging.

Appellate Division Judges Edith Payne and Alexander Waugh Jr. agreed, pointing to Gardner’s general power to review SAVA investigatory files and assign cases to prosecutors as well as his participation in discussions about the investigation and his “actual knowledge of the crimes … imparted through the Chief Sheets.”

The panel cited In re Advisory Opinion on Professional Ethics, No. 361, 77 N.J. 199 (1978), which held that an assistant county prosecutor involved in an investigation is per se “foreclosed from representing in that or any related matter any person who had been the subject of the investigation or is indicted or tried as a result of the investigation.” Any actual knowledge or “responsibility, whether exercised or not,” disqualifies the attorney, the opinion continued.

The panel also quoted from a 1983 state Supreme Court case, Ross v. Canino, 93 N.J. 402, which held that “a former government attorney will be disqualified if he was substantially responsible for an investigation even if he did not exercise that responsibility.”

And the panel cited Ethics Opinion No. 614 (1988), which found that “the active exercise of responsibility for the matter such as making a decision with respect to a matter of substance will qualify as ‘substantial responsibility’” as used in the RPC.

The panel agreed with Gardner that Rivadeneira has the right to counsel of his choosing but not where it “will obstruct an orderly procedure in courts of justice and deprive such courts of the exercise of their inherent powers to control the same.”

Assistant Hudson County Prosecutor John Mulkeen says, “We’re ready to proceed with replacement counsel,” provided Gardner does not petition the state Supreme Court for certification.

Neither Gardner nor Camacho, who argued the case on appeal, returned a reporter’s call.