The Cato Institute has a map detailing botched S.W.A.T. raids over the past 2 decades.  These are incidents where the police often needlessly used para-military force to conduct no-knock raids that were conducted on innocent suspects and ones that ended in tragedy.  Last year alone in New Jersey, S.W.A.T. teams with the wrong addresses raided four innocent families--luckily, none ended in tragedy.

 via Twenty Thousand Tonnes of Machinery