"temper as hot as my forge".
Quite like that personally
How about:
Unyielding as the Iron I Forge - You're tough and inflexible, both physically and morally, the rules are the rules and that's the way you like it.
For want of a Nail - "For want of a nail the shoe was lost, For want of a shoe the horse was lost.....For want of a battle the kingdom was lost, And all for the want of a horseshoe nail." Sometimes you forget things, usually they're insignificant and don't particularly matter, but occasionally, just occasionally they can snowball into a major problem.
Between the Hammer and the Anvil - When there's a conflict you're always there right in the middle of it, forced to make tough choices, not by design, but by Fate.
Other iron's in the Fire/
Too many iron's in the Fire - You're a multifaceted individual with diverse interests and hobbies, sometimes this can cause problems as a multitude of niggling minor issues can draw your attention away from the big picture.
The curious case of [Insert Holmes-esque title here] /
The one that got away - You are haunted by a past case, whether it was unwittingly(or deliberately) sent an innocent to their death, losing the perp, or getting your partner killed, you can't put the events behind you.
All Crimes are Equal - Some people say that the world exists in shades of grey...For you everything is White or Black, Right or Wrong, Innocent or deserving of...Punishment.
By any means Necessary - If you're on a case, you're gonna solve it, no matter what it takes, no matter who you have to kill, what you have to destroy, no matter the consequences...
The Chief's favorite doormat - Some time in the past you REALLY pi**ed off the boss, maybe you slept with his daughter, maybe you scratched his car, maybe you just put the wrong number of sugars in his coffee, but he just LOVES to give you the worst jobs, partners you with the greenest rookies, dumps backlogged paperwork on you around the holidays and generally makes it his life's work to scr*w with you.
Watchman...Unwatched - Who watches the Watchmen. In your case, no-one, you work almost entirely without supervision, great for when you need to bend (or break) those pesky rules. But when you need official backup there's usually somewhere more urgent that they need to be.
To know him, I must become him - You have an instinctive knack of understanding the criminal (lawbreaker) mindset...Maybe a little TOO instinctive...Hmm, doesn't that power look mighty tempting.
I've found that a good place to look for inspiration is in the categories section of
, those trope titles are almost always aspectworthy.
edited:link put in spoiler tag as requested and cleaned up some of the text.