If you're talking about the event in Atlanta, you've missed a few details.
They had a warrant, it was just obtained with false information from information provided by an informant who was know to be not credible.

You've missed a few details as well - the cops arrested a small time dealer who claimed that he saw cocaine in the house that the grandmother lived. The cops got a warrant based on a supposed "confidential informant" (which was not true, it was just someone trying to get out of their own bust). They lied to get the warrant. When everything went bad they found a CI that they had used before and pressured him into lying and saying that he bought drugs from the woman and then the cops also planted drugs in the woman's home. The cops did not follow proper procedure, they didn't want to find a true CI, they just wanted to bust right in with no real proof. Good thing those cops are going to jail.