This time, the anti-terrorist military unit sent to stop the bad guys turns out to be made up of more bad guys -- the machine guns they had used to shoot each other were filled with blanks, to fool onlookers. McClane finds this out, storms into the airport police station and shows one of these incriminating guns to Captain Lorenzo (Dennis Franz) to secure his help.
And by "shows" we mean "fires the gun directly at him." In a room full of armed cops. On the day that terrorists took over the airport.
"Holy shit! Someone call the cops!"
Yep, that should have been the end of the Die Hard franchise, right there. Sure, the gun was filled with blanks, but the cops around McClane didn't know that -- all they saw was some crazy guy shooting at their boss. If a single one of those cops had done their job (that is, placed a bullet on McClane's face), then who would have stopped the next four or so terrorist attacks/heists against America and Russia? Argyle the limo driver?
Did all the cops fire blanks at him, too? Plot twist!