Warning: contains spoilers for Batman '89 #1!
Batman is a ruthless killer in his latest adaptation of a classic iteration. The Caped Crusader beats up criminals left and right, breaking dozens of laws every night, but he very famously never kills his enemies. This changes in Batman '89 #1, written by Sam Hamm with art by Joe Quinones and colors by Leonardo Ito, in which Batman is an unapologetic murderer - just like the source material.
Batman '89 is a 2021 miniseries based on the 1989 Tim Burton film of the same name. While it wasn't the first cinematic adaptation of the Dark Knight (that honor goes to the Batman film serial released in 1941), it was the first to adapt Batman's dark and gothic's modern incarnation. Burton's film was a critical and commercial success at the time, spawning four sequels - but Burton famously left the series after Batman Returns. Batman '89 is partially based on the director's plans for an unmade followup, including roles for Marlon Wayans and Billy Dee Williams as Two-Face. But some of Burton's creative liberties made some fans very upset - namely, Batman kills.
On a Halloween night, Harvey Dent invites Barbara Gordon to dinner with the intent to propose. The question is asked and the ring is in his hand when an explosion disrupts the evening; a gang of Joker lookalikes force two armored trucks to collide on the Gotham City streets. A helicopter (also piloted by members of the gang) arrives to lift the trucks, but the pilots encounter a problem: Batman has arrived, and using his grapple gun, hooked the helicopter to a nearby building. The pilots try to correct, but it's too late: the helicopter collides with the building and is engulfed in a massive explosion...along with the pilots.
Both pilots are almost certainly dead and Batman's to blame. This would hardly be the first time that Tim Burton's dark knight has killed his enemies. In Batman, four henchmen are caught in an explosion at a factory that Batman himself caused. In Batman Returns, a henchman attempts to kill Batman with a bomb...but Batman ties the bomb to the henchman's belt before kicking him down a manhole. Viewers are treated to an explosion as Batman calmly walks away (with a sadistic smile to boot). Thus, Batman's killing of the pilots may be entirely in-character with Michael Keaton's Batman, but it's still quite shocking to readers used to Batman's strict no-kill policy.
While Batman's primary objective was stopping the helicopter, surely he knew the pilots would be caught in the explosion - but this Batman sheds no tears and indeed, gives no thought to unnamed henchmen. Writers have toyed with the idea of Batman abandoning his one rule (most notably Zack Snyder in Batman v. Superman: Dawn of Justice), but while many aspects of the character have changed over the years, Batman's one rule is as crucial to his character as the cape and cowl.