If you didn't have any weed seeds or plants, they shouldn't have taken anything. It's not illegal to own grow supplies.
Merely owning grow supplies isn't illegal, but "attempted cultivation" most definitely
is illegal.
Exactly where the line is that constitutes an "attempt" is something that lawyers earn their money arguing about in courtrooms, and it can actually vary from jurisdiction to jurisdiction. Still, I think a pretty good case could be made that if you had what amounts to a complete growroom setup, just minus seeds, you've already gone enough of the way there that you've satisfied the legal definition of "attempt".
Just owning a bunch of growlights in boxes and pots? Probably not enough for "attempt", but again, that's something left to lawyers, judges, and juries.
In any case, if the cops took all your grow equipment, and didn't charge you with a crime, then to me that's simple theft.
Tough talk about charging you with a crime if you try and retrieve your property is just that. They're probably just trying to intimidate you. If they think they have enough evidence to charge you, why haven't they done so already? (Answer: they probably know its a weak case, at best). If they've seized your property as evidence, then what right do they have to destroy it? Destroying evidence is ITSELF a crime!
If you want your stuff back, go consult a lawyer. I think you probably *could* get it back this way, though now its a question of "is it worth it"? Lawyers cost money, of course, and the cops will probably try to stonewall, meaning it may take quite a while before your stuff is actually returned.
Unless you're talking about thousands of dollars of expensive equipment, probably the wisest thing to do here, is to let it slide, and get the heck out of their jurisdiction. Even if you sue the cops to get your stuff back and "win" you'll still probably "lose" because the cops can harass you in all sorts of legal, quasi-legal, and illegal ways, and if they decide you're a "troublemaker" they just may want to do that.
This is going to sound "crazy", but if you look at this from the cops perspective, they've actually just done you a huge favor by confiscating your stuff, even if what they did was technically illegal. They've stopped you from committing a felony, AND they didn't charge you with a crime.