I don't know where you get your information. They didn't just bust into his backyard without a warrant for no reason. If there is a crazy psycho running through your neighborhood, and he runs into your house, and into your illegal grow room with the cops just behind him, they DO NOT need a warrant to enter your house, and anything they find they can use against you.They did not do anything because they did not have "right's" to be in your yard and observe the plants. They were chasing a suspect whom ended up in your yard, they are allowed to chase into private property.
Even if you were doing lines off an illegal immigrants ass while waiving your black market AK in the air when they came in. They probably would have taken you to jail but you would walk out the same day and the charges would never stick.
They were probably discussing if they can see the plants or smell them without being inside the yard so they could attempt to pursue you.
Find a collective in your area, allot of good people will rescue plants in need of a temporary or permeate home.
.....................If they didn't ask you for your card immediately I doubt they care. It's not like you had a forest in your backyard.
You can always claim they're your sisters' plants since she's legalI did end up keeping the plants and the cops never returned. I kept a copy of my sister's medical marijuana card in the backyard near the plants. Thanks for all the input. I for sure am getting me a card before I grow again. Definitely not worth the stress and worry.