Good evening,
There is quite a few things to go over with this but ultimately it is getting denied and I'll elaborate on every point to clear up any confusion.
1. Suppressors do not make gunshots unable to be heard through buildings, guns are very loud and suppressors do not make them "silent" or unable to be heard, the only mechanic for guns that isn't allowed to be used in RP in terms of sound is the loading sound that plays when you equip more ammo.
2. The cop did in fact hear the gun shot and this was not a personal ploy against you. They were staking you out longer than you had known, and did hear the gunshot from when you murdered the man. There was no underhanded tactics at play, the officer was simply camping out and you missed them.
3. Having a dupe up does not make any noises from your room invalid, you fired a weapon in a very small room, a "barrier" on the window would not dampen this noise nearly enough for people, or in this case the police, from hearing gun shots. In the evidence from the police side provided to me they very clearly see you put up the dupe, and there is no question as to what room the gun fire came from.
I understand with a skewed view how you may believe this situation to be powergame, but after getting both sides and reviewing all the evidence there was no abuse of game mechanics to get an upper-hand on you and your associate, rather a lack of awareness led to what happened in this situation. In the future, please be aware that suppressors are not the end all be all in terms of avoiding detainment, and it is still a very loud gun being fired in a very tiny room.