ummm…. I guess that would work too...
How about a tank of carbon monoxide, set on slow leak.
Holy shit, that's a dangerous thought.
http://www.ncbi.nlm.nih.gov/pubmed/7124129
There were 1,985 fatal cases of CO poisoning in the Tohoku district of Japan in the period from 1969 to 1980. Among them, 1,322 cases were suicidal, 662 accidental, and one homicidal, in which a man killed his wife with the self-made CO gas to obtain by fraud a large amount of life insurance. Our nationwide survey revealed four other cases of homicidal CO poisoning and two cases of camouflaged CO poisoning. The police and police surgeons should be cautious enough in cases of CO poisoning.
Only one homicide? I find that hard to believe.
Yes, they carry it but don't develop AIDS, happens in Africa where people have immunity for many diseases already but not the rest of the world:
http://www.nytimes.com/2000/02/03/us/a-new-aids-mystery-prostitutes-who-have-remained-immune.html