Headscratchers / Lethal Weapon 4

• Why in heck does a dental office have laughing gas?!
  • Nitrous Oxide - in supervised, controlled doses - acts as a tranquilizer for anyone who is having a tooth pulled. Dentists, or orthodontists who need to do such procedures, will require that the patient have someone to drive them home afterward, as the effects of the gas - which vary from patient to patient - take a while to wear off.
    • It's practically the default in most offices that treat children, as it calms them before the needles go in. And it is used for adults who may require it as well. If you hear of a dentist that practices "sedation dentistry", that's usually what they are talking about. As a person with phobia level panic attacks when going to dentists (it requires valium for me to even walk in the door), they use this on me for anything more than a cleaning.

• Was it ever explain why the guy with the body armor and assault weapons was shooting and burning things up? Does anyone know what his deal was?
  • It wasn't explained (at least not in the film itself), so it's up to you as to how to interpret it. He doesn't look like a "meet my ransom terms or I'll destroy this city block" terrorist to me. I think somewhere in that area was his former place of work and he's just trying to torch it because he's disgruntled about being fired. Of course, because he's so up-armed and up-armoured, he may have had the intention of trying to escape after carrying out the rampage.