This is actually a very important moment. He does'nt kill the Banker, when the Jokers says that, the Banker shows that his gut is'nt full of bullitt holes (some kind dart puncture) , and the grenade in his mouth is a smoke grenade filled with the modified toxin we saw that the scarecrow unleashed on the city. When the Joker says "stranger" its sounds weird in the way when people were tripping out at the end of Begins. So the Joker was going to use this toxin to build an army of basket cases to overun gotham. Gambol, was 'nt killed (unless he died of fear), The Joker put a smile on his face. When he breaks the pool cues in half and prepares for Gambols goons for "tryouts" he's also lookin down at Gambol when he says the word. The Batman Impersonator went through the same ordeal but was'nt strong enough. If you slow the DVD down the scene where the Joker is in the nurses uniform and shoots the cop it is not with any bullets but if you slow it down it's some kind ?tranquilizer? dart. In the Jokers twisted plan he's going to "reform" these people in building his "army". After Batman crashed his bike and is on the ground he unleashes the knife not to remove the mask, (he already knows he's Batman) he's going to convert him with a smile on his face. Him too he is giddy to recruit to his "army". "Kill you hehehehe what would I do without you! no, No, NO! what would I do without you. YOU complete me!"

On a separate note Rachel Dawes does NOT die. There is an explosion from the building next to her that gets her hair mussed. But then there is a explosion at about the same time at the precinct next to the building the Jokers in that gets debris all over him. She's overlooking a Harbor, the place, the address Joker gives to Batman/Dent, there is no Harbor in the background. The following scene that Batman is at, the burned out building, finds the Dent coin. He finds no body. The scene after that you see the Joker leaving the Police Precinct in all his glory, if you look closely there are two people in the car. One is Lau. The other which is the driver looks like a woman with disheveled hair. Rachel could be the driver . Before that at the procession of the late Commisioner Loeb, the handcuffed fake cop arkham alumn Thomas Schiff (who has a resemblance to the Scarecrow) is wearing a "Officer Dawes" tag and tries to draw attenton to it. Somehow she fits into his plans. Before that scene in the Penthouse, she looks on him with no fear and with sympathy. Moments before at the beginning of the party Harvey Dent tells Alfred "so you've known Rachel her whole life?" he say's "Not Yet". A intriguing foreshadowing of a potential hint in the script of Rachels trials. Before that let me go to end of Batman Begins the little boy in the Orange Shirt , the narrative of the Joker begins there. He's not the Joker of course but hes come from the financial and social status (broken home) the Joker woud have come from . Rachel protects him. Now the scene where the Joker is revealed to Batman behind shows orange color over Gordons left shoulder and he moves forward the purple of the city lights comes into light next to Batman's right shoulder. The Joker would have sympathy for someone like him and his social and tough upbringing. There is evidence the Joker is recruiting people from Gordons unit like Ramirez. He may know have investigated her learning of her looking out for that little boy and upbringing and know shes not corrupt like the other goons-"I'm a 20 year man..." " Its my own fault shoot him!" The Joker would not have Rachel Killed and would not be given access to the crime boss'. He thought he and Batman were similar and he was trying to make a sign of kinship and prove he's not a monster and would prove it in securing her safety. Of Course we will never know I hoped these would be revealed in a third film. The Joker fading into oblivion just made it impossible. Maybe she would be a fascinating Harley Quinn?hhhhmmmmppp "just a head of the curve" :modesty: But, I refuse to believe AND I know she was'nt killed in the Dark Knight. Katie Holmes was great , Maggie Gyllenhall was great I refuse to believe that great character went out like that. The Joker would'nt do that. He's a higher class of criminal.

Just one thing:

and the grenade in his mouth is a smoke grenade filled with the modified toxin we saw that the scarecrow unleashed on the city.

How can you be sure about that?

Circumstantially 1. The Jokers voice sounds like the Scarecrows and when he say's "stranger" as you hear it from the bankers point of view. 2. That's why he screams like a monster to the Batman Impersonator.
3. The Scarecrow was able to weaponize the toxin and disperse it in Batman Begins before Ra'as Al Ghul arrived (Falcone: "you mean he's coming here" Crane:"Yes he is and he's not going allow us to jeopardize our operation just to get your thugs out of a little jailtime "
4. as Gordon say's they still had'nt found Crane in his Bat symbol meeting with Batman at the end of Batman Begins, the Scarecrow is still active in the time in between movies, acting as a drug dealer in his scene in The Dark Knight ("Russian Gangster: Look at what your drugs did to my customers")
5. Proof that the Joker has contacts with Crane is evidenced by his videoing of Ryan Duckworth/Batman impersonator (they were restrained tied together and abandoned by Batman in his opening scene in the movie)
Batman stopped a catastrophe when he sabotaged the train in Begins , but the death of Ra'as Al-Ghul did'nt put a hamper on there plans
6. the main point with the final scene of Batman Begins and the introduction of the Joker is escalation
7. My favorite hint in the movie is at the penthouse when the Joker arrives he eats an hours d'ouevre and looks to grab some champagne to wash it down and he purposefully spills almost all of it with a little smile, drinking the sparse amount left. (the Joker douses alcohol with his strain of toxin to increase the rate of people losing there mind, due to his traumatic childhood experiences with his father ("My father was a drinker and a fiend...)) In a scene prior to that after Bruce Waynes "I Believe in Harvey Dent" speech he walks out to his patio and dumps his glass of champagne very much experienced with the effects of a weaponized hallucinogins, he suspects
8. Gordons kitchen at home is illuminated by a green light and his wife makes weird noises when she gets emotional either a mutated laugh or just freakish.
All subtle , but I think there was a axis chemicals subpplot seeds being planted for the third film, that had to be drop when the return of the Joker was off the table.
9. Remember the Joker prophetically said that rate of people losing there minds would double. Escalation.