Unlike most cases of police corruption, there is direct evidence of their misconduct that could be used to convict them. Every time corrupt cops filed false reports, they put their names on them. The US's DOJ is not charging those corrupt cops, and by not doing so they are condoning further corruption.
In Settlement, Newark Agrees to a Series of Police Department Reforms
Federal officials announced on Wednesday that a sweeping settlement had been reached to reform the Newark Police Department after a three-year investigation uncovered a pattern of unconstitutional practices, including improper searches and stops and excessive use of force.