I so totally know what you mean when you talk about getting ass-kicked by the query. I swear it's harder than writing a hundred novels!
Anyway, while I agree with most of the earlier suggestions to your query, I do have to speak up and say I thought the first line of your original query was a great hook (with a few edits):
To me, this is an engaging, unusual hook that made me read on -- but that's just me.When an Assistant D.A. is murdered, Detective Ethan Moon finds himself hunting a killer he knows, loves, and misses--and thought was already dead: his brother.
I really like your second paragraph, but would suggest edits as follows:
The last paragraph I think should focus on the choice Ethan faces and the stakes involved -- e.g.:Ethan expected a normal case, gather evidence, talk to witnesses, follow leads and catch the killer; The investigation proceeds routinely until a videotape found at a treatment center shows his brother is alive, and is the killer he's hunting. A radical therapy program has turned Ethan's brother into a weapon, wielded by a corrupt Senator at the head of a human trafficking ring.
Those are far from being wondrously perfect sentences (gag), but my point is to describe the choice and the stakes, not tell how the story ends. (After all, the point is to entice the agent to read the novel!)When Ethan discovers his brother is being used against his will, he must choose between bringing the murderer to justice and losing his brother all over again, or fighting the corrupt senator and risk losing his own life to save his new-found brother and the young nephew he never knew he had.
You've far exceeded my efforts at coming up with a good query -- nice work and best of luck with the query!
Joan