From my understanding of how it was said in the past is that someone would need to figure out it was you. There will be a forensics skill line for investigating and if I remember correctly, evidence could expire.. Which makes me think of footprints going away due to rain or wind. It was also said that evidence of your crime could be discarded so if the person isn't good at figuring things out even though his character is, he could miss important clues. It could also be used by a corrupt person to cover the tracks of their friend or client.
As far as poisons, you could poison food or drink, even a well. Weapons were still undecided on. It was also not confirmed if there would be a poison strong enough to CDG or if it would just be KO's.