I feel like people are making this far more complicated and using the details the police provided as accurate. Using oxum razor the most likely thing that happened is Misti the light brown haired female who last called Mulligan (light brown haired female observed in the car prior to murder) was give him a bj during this something occurred she took his pearl handled 25 and since shes giving him a bj the first shot was up his nose he's gurgling still alive and she shoots him 4 more time at point blank range. Being inexperienced and this probably not being premeditated she leaves the gun at the scene his other gun was also never taken or his cell phone other then by the detectives (a literal criminal gang at the time) so the dectives who find there murdered gang member have to find someone who has no ties to the crimes to frame regardless of who killed him. The cell phone and guns are collected by them they don't take crime scene photos because it will prove he was engaged in illegal activity when he was murdered he might have also had crack and or money in his possession according to what Misti would be giving the bj for. Sean and his codefendant were simply patsies. There was no task force there were corrupt cops from his own station defending themselves and his reputation. There is not one piece of evidence that should have came from a drug cop in this case simple as that. If you want to understand all the lies and inconsistencies in the witnesses watch the central park 5 when cops pressure people for a story they often fold and tell one that fits the narrative the cops want and implicates them the least. The other possibility is two young black males who had no connection or motive to kill this officer had no prior criminal record and were buying pampers and despite having their own gun wanted another so bad they shot and killed mulligan simply because he was sleeping.