9. The Justice League Learn Who Killed Sue Dibny - Identity Crisis #1-7 (2004)
Sue Dibny was the wife of Justice Leaguer, Ralph Dibny, better-known as the stretchy superhero, Elongated Man. One of the darkest moments in the team's history is when Ralph came home to find the charred corpse of his wife.
When the Atom's ex-wife, Jean Loring, was nearly strangled to death, the Justice League theorise that someone deduced their secret identities and was attempting to pick off their loved ones.
While examining Sue's corpse, Doctor Mid-Nite finds two microscopic footprints on her brain. He reasons that someone shrunk themselves and entered her brain, causing her to die from an aneurysm. Because the killer used shrinking technology, the prime suspect is the the Atom, Ray Palmer.
However, Palmer figures out that the real killer is none other than his ex-wife, Jean. Although they had been divorced for years, Jean realised she wanted Ray back. She used Ray's Atom suit to murder Sue, and then faked her own attack, hoping it would make Ray come running back to her.
It's horrifying for the reader to look at Ray's face as he acknowledges his ex has murdered one of their best friends. Left with no choice, Ray had Jean institutionalised in Arkham Asylum.