The trailer begins with a wheelchair-bound Jason Todd meeting with Dick Grayson, and he tells him that Batman is in trouble. The scene switches to Gotham, which Todd says has gotten even worse. In fact, it's gotten so bad that Todd tells Grayson Commissioner Gordon has been killed, and the next scene shows a variety of cops on the street around a body that looks to be Gordon.
It's after this that Todd tells Grayson Batman is going to kill the Joker, which implies that it is the Joker that killed Gordon or at least had something to do with killing Gordon. This could be the death that puts him over the edge, and by the looks of the rest of the trailer, he really has gone over it.
You can find out more about the new trailer here.
Granted, it isn't like Batman needed more ammunition in his want to kill the Clown Prince of Crime. Joker has killed plenty of people during his crime sprees, but at least in this version of the Batman mythos, it doesn't appear that he's killed a Robin yet, so Gordon would be the most personal attack Bruce Wayne has suffered.
Adding fuel to that fire is the fact that Todd is in a wheelchair. Perhaps Joker had something to do with that too and having his sidekick brutally hurt and his longtime friend and supporter Gordon killed would definitely be enough to push the Dark Knight to vengeance. From the trailer, though we can see that his vengeance doesn't stop with the Joker, as bloody shots of Two-Face and The Riddler are shown, as well as plenty of other bodies, not to mention Joker being put through a car windshield.
Yeah, he's probably not getting up from that.
Titans stars Brenton Thwaites as Dick Grayson/Robin, Teagan Croft as Raven, Anna Diop as Starfire, Ryan Potter as Beast Boy, Alan Ritchson as Hawk, and Minka Kelly as Dove. Other cast members will include Lindsey Gort, April Bowlby, Jale Michaels, Dwain Murphy, Seamus Dever, and Bruno Bichir. The series is being produced by Geoff Johns, Greg Berlanti, and Akiva Goldsman.
"Titans follows a group of young soon-to-be superheroes recruited from every corner of the DC Universe. In the action-adventure series, Dick Grayson emerges from the shadows to become the leader of a fearless band of new heroes that includes Starfire, Raven and others."
Titans is available on the DC Universe app now and updates with new episodes every Friday.