Booster's forcefield

The more I think about it the more it bothers me.

SPOILERS AHEAD

We don't know who the murderer is but I'm willing to give the benefit of the doubt that DC isn't doing something stupid like making Booster the killer. From what we know so far the attack started in Sanctuary with most of the patients fleeing out the door to be killed in the field. Roy and Wally were inside, maybe they were fighting off the killer. At the moment it seems like they were the first to die.

A lot doesn't make sense yet like why a group of heroes didn't overpower what we presume (at this point) is one killer. Why didn't Wally get everyone to safety? But I'm confused why Booster's forcefield didn't come into play. Not in his fight with Harley, which would be logical if he didn't want to hurt her or others, or apparently during the murderers' killing spree. Right now everyone seems to be suggesting the victims were killed by bullets. Which wouldn't make sense because Wally should be able to stop the bullets so I'm expecting more.

Booster's forcefield is able to withstand a lot thanks to it being created by Brainaic 5. If it was a projectile weapon he should have been able to block it easily yet his damaged costume looks like it either didn't work or he never used it. Am I just over thinking this and King simply forgot about it?