Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Depending on the concentration of carbon monoxide death would occur anywhere from 2 hours to less than three minutes. Injection occurs by inhalation and being colorless odorless tasteless and initially non irritating it is difficult for people to detect. Seems to meet all his requirements unless I missing something