A 15-year D.C. police veteran who was instrumental in the undercover investigation of Andrew James McGill Jr.--the officer accused of decade-long involvement in a drug trafficking ring--was transferred out of the internal affairs unit this week because of a misconduct charge, police said.

Detective Joseph Twiggs, 37, was moved out of the unit, which polices the conduct of other officers, and transferred to the 6th Police District on Monday in what was called a "lateral move" by Executive Assistant Chief Terrance W. Gainer.

Twiggs was transferred again yesterday, to the 2nd Police District, after saying he felt uncomfortable in the 6th District and would be more effective in the 2nd District, Gainer said.

"Given the fact that he had worked against several officers in the department, he requested 2D," Gainer said. "We wanted to accommodate his concerns."

Because Twiggs's misconduct was unrelated to the drug investigation, the case against McGill has not been compromised, Gainer said. "Nothing he has done . . . undermines his integrity," Gainer said.

Gainer also pointed out that the investigation was not conducted solely by D.C. police. Several federal agencies also were involved, including the Drug Enforcement Administration, the FBI and the Maryland U.S. attorney's office. McGill was indicted in the case by a federal grand jury in Greenbelt.

Gainer would not say what the alleged misconduct was and said the matter was all but resolved with the transfer. Although Twiggs's actions were substantiated, he was not disciplined, Gainer said. "We know what we know, and we did what we had to do," Gainer said.

According to court records and law enforcement officials, McGill, 29, was part of a drug network that trafficked in heroin, cocaine and marijuana for more than a decade. His involvement allegedly began when he was at the police academy and evolved over a 10-year career that included a stint as a narcotics investigator.

Because of the sensitive nature of the investigation, which is continuing, many of the records in the case are sealed in U.S. District Court in Greenbelt. McGill was arrested Jan. 6 on federal charges of trafficking cocaine beginning in 1989.

Twiggs's alleged misconduct was brought to Gainer's attention about two weeks ago by the director of the office of professional responsibility, Inspector Dwight Williams. After a preliminary investigation, Gainer decided to have Twiggs moved.

Twiggs, who had "direct involvement" in the McGill case, will now investigate violent crimes in the 2nd District, Gainer said. Lt. Joseph Trippi, who heads violent crime investigations in the 2nd District, said he had not seen Twiggs yesterday.

"He's [Twiggs] a seasoned investigator who has a very good reputation in the department," Gainer said.

CAPTION: The transferred detective was involved in the probe of Officer Andrew James McGill Jr.