It definately gave them an edge, you gotta admit that.
I think the basic problem is that 1) Only one person was in on the plan and 2)they expected things to work out according to their plan perfectly.
Were it me, I'd have rigged that sword so it couldn't be used against me and had a bomb set on a deadman's switch that would take out two city blocks if triggered.
After all, there is no overkill. There is only 'Open Fire' and 'I need to reload'.