Douglas L. Young, the attorney representing one of the four defendants accused of murdering Los Angeles Police Detective Thomas C. Williams, was found to have a conflict of interest with the suspect and was removed from the case. Duane Moody, 27, of Los Angeles, who is charged with murder and conspiracy in the Oct. 31 Canoga Park shooting, will be represented by James M. Epstein, who was appointed to the case by Van Nuys Municipal Court Commissioner Patricia G. Schwartz. Moody dismissed Young after the prosecutor announced Friday that two of the witnesses who will testify against Moody are business associates of Young. The two witnesses are making a movie about one of Young’s clients and claim to have overheard Moody say on Oct. 16 that he “would kill” the detective if he testified in the robbery trial of Daniel Steven Jenkins, 30. Jenkins, who was free on bail at the time, is suspected of being the triggerman in Williams’ slaying.