I hate those type of bûllshît in mangas and movies... even if you shòot someone with a silencer, it still make a lot of noise... it’s almost impossible to not hear that . The scenarist should at least try to shòt with a gun to try and see !!!
Overall, there are a lot of plot holes in this manga. Like nobody tried to search the helicopter crash or look for guns from the armed guys on the beach