I 100% understand how you feel. It's ironic that the dog that killed your beloved little Seramas was also a white Shepherd mix. Your description of that evil mutt could also describe the foul creature that killed two of my most beloved girls last autumn.
I'm in total agreement with one of the other posters that said you needn't tell authorities that you have roosters. Just showing them the bodies of the hens should be sufficient. The important thing at this point is to document the loss. This way, when that wretched creature returns, you'll have a history with your local animal control department and they'll know that this is a recurring problem and that they need to address it immediately.
How many of your birds remain? If there's even one, you know it will return.
I had to resort to penning my girls in a large enclosure, where before they had been allowed to range freely over 10+ acres. It's not fair! My birds
NEVER left the farm. Never bothered anyone. Neighbors have always enjoyed eggs from my girls. They've been an asset to the neighborhood.
Then along comes this wretched dog, and an equally wretched owner (I blame the owner entirely here. The dog was just doing what comes natural when they're neglected and left to pretty much fend for themselves!) and my girls are the ones who pay the price of the irresponsible dog owner.
Lost my two very best ladies to that *&%#@(! animal!
I hope you catch that darn dog! Turn him over to the animal control authority in your area. Don't even bother talking to the owner, even if you did know who they are. If they're irresponsible enough to let their dog wander free, then it's a pretty sure bet that they couldn't give a rip about someone else's chickens! Like you said, people who don't have chickens will never understand how deep the attachment and love can go for these feathered friends of ours. So, don't bother beating your head against that wall!! Just let animal control handle it! If you complain long enough and loud enough, they have no choice but to deal with you, and subsequently the dog! You'll be doing yourself and anyone else in your neighborhood who has chickens a huge favor!
And yes, we're still watching for the return of that horrid dog to our coop. He's just about due in fact. **checks the shotgun loaded with salt to make sure it's still ready for that inevitable day** Yup! We're ready for HIM!!