If you want twelve dead hostages then sure
He might kill them regardless.
Why do people think that someone like this will "do the right thing" when, if they did the right thing before, they wouldn't be in this situation?
Someone who carries a gun and holds people hostage is not likely to be the most honest and trustworthy person. So why do we think he can be appeased?
I say,if it is one perpetrator, draw him to the window, and get a police sniper to take him out. Then rescue the hostages.
Who cares if civil libertarians cry about you taking out the perp? People should be thanking the police for rescuing the hostages, not condemning them if they shoot the crim.