I hadn't heard about this so googled it...
http://www.globeandmail.com/servlet/story/RTGAM.20040525.wbuss0525/BNStory/National/
>>Police believe the substance may be a gas called phosphine, which is an industrial gas used as an insecticide and for pest control.<<
Thanks for the links.
I see the reference to phosphine, not phosgene.
My poster also said a reporter 150 meters away from the bus became ill - but I suppose this could have been a hysterical reaction.
Both are deadly. Both are fairly easy to make.
Phosphine is an industrial gas available in compressed gas cylinders from lecture bottle size (not much bigger than a spray can) to rail tanker car. I've used it as a phosphorus source for semiconductor doping. IIRC, it's about 40 times more toxic than cyanide.
Phosgene - Carbon Monoxide Chloride is a war gas. Very nasty In contact with moist lung tissues it forms hydrochloric acid which damages the lungs. They fill up with fluid, the victims start drowning in their own fluids.
It also liberates Carbon Monoxide. What little oxygen the victims does manage to get into their lungs finds the hemoglobin bound up, the blood can't carry the oxygen to the rest of the body.
Very nasty.