Take one cigarette...make it half empty and place a medical needle (which is hollow) in it, previously dipped/filled in some poison that can resist heat (probably potassium cyanide), and then fill the top of the cigarette with the rest of the tobacco, just enough so the top of the needle can be at least few centimetres out. When you locate your target in some club or party, light the cig (DONT INHALE) and quickly go next to him or her and make it look like accidental cigarette burn because of the packed location. Say "sorry" and walk away (you might get hit but "sorry" is enough, including the act as a scared individual). After that, theres at least 80% chances that the target will start feeling dizzy and if he/she dies, at the autopsy they wont be able to find the puncture wound but instead, they'll see a simple cigarette burn and chances are they might think that the victim was poisoned via drinks, meaning you're off the hook.

At least this is how some of the government agencies used to or still "work" in the same or similar style .