A police raid was performed on Subs 11, which Aaron and many others used to grow. During the police raid, everyone from the house showed resistance and began firing upon (and killing) the majority of the police force. During that, 4 pots were picked (3 of Aaron's, 1 of Walker's), despite the situation being far from done, which can be seen as they were killed shortly after.
It is quite obvious that the scene was not yet secured, as cops were still dying left and right, with still many of the defenders alive.