I think everyone will have their own suggestions. I've been dealing with predators too, recently had my coop ripped apart by a bear so FYI, almost nothing is bear proof. However, using 1/4" hardware cloth that is screwed in using strips of wood over the hardware cloth is most effective against being torn, or small paws reaching through. A locking latch, or a latch with a lock on it is most effective against raccoons, which are very intelligent. Finally, surrounding your area with a simple electric fence will likely deter anything from even getting to your coop in the first place, including bears. You can buy at TSC nearly everything you need for under $150-$200. I bought fiberglass rods so no need for insulators and super easy for my 95 pound self to drive into the drought hardened ground, a 30 mile controller, strong enough for cattle (and theoretically bear), and 17 gauge wire. You will also need 8 or 9 gauge wire and a copper rod for a grounding rod. Copper only needs driven in about 3-4" where an iron rod needs to be much deeper. I was clueless about how to set this system up until someone told me what to buy, and from there it was a cakewalk.
I am so sorry about the loss of your birds. Two days after my bear attack, which didn't kill any chickens, I had a daytime predator kill one of my hens. Likely a coyote. On that same night our neighbor lost 12 hens to the bear and it has since returned to their farm. I can only assume my electric fence is doing the job. You can also buy noise makers which are decent at deterring daytime predators. I wonder if, because the door was open, your problem was a racoon.
Here was the coop after bear attack. My hardware cloth was only screwed in. Nothing to a bear! The boards to the nest box were actually ripped in half.
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The bear had less success in the back. It's unbelieve the strength that he had. Ripped a door clear off its hinges!
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Here is the repaired coop with the fiberglass poles, and 17 gauge electric wire ran in three layers, but short enough for me to step over carefully. This time I covered the poultry wire with strips of wood and used 3" wood screws. I reinforced the remaining parts and repairs using either 3" or 4" wood screws.
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I think you can see the electric fence better from the back. I turn it off during the day. All repairs and fencing were done in a single day. Pictured is my black cochin. Sadly she was the one taken by the daytime predator
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I wish you the best of luck, and again I'm so sorry for you and your little birds