Yes, I believe that the police in Chicago are very corrupt because there has been a lot of cases regarding the shootings of unarmed men and also most murders in Chicago usually go unsolved. I believe the Chicago Police Department isn't doing enough to curb violent shootings and crimes in their neighborhood.
Time and time again, we see that the actions of one person or one small group become exaggerated and are seen to the uninformed eye as the actions for a larger group. We cannot know that just because the Chicago police accidentally destroyed a note that this means the majority of Chicago police are corrupt. This extrapolation can not be made nor confirmed from this data.
No, most police in Chicago are not corrupt. The police in Chicago that do bad things make the news. There is no reason to put a story about a police officer in Chicago who did not do anything wrong on the news. Therefore, all of the new stories are bad but most of the police are not.
While it is very likely that some police in Chicago are corrupt, it is more likely that most are not. In fact, corruption affects all groups at all levels but that does not mean that most of that group is corrupt. Police officers are human, just like the rest of us, and mistakes happen. While they still need to answer for those mistakes just like everyone does, it is unfair to say that because mistakes happen they are all corrupt.