Well there's a fundamental difference between a carnivorous plant and a murderous plant who just kills.

There are many plants who kill large number of animals all the time, as defense measures for example. But a carnivorous plant specifically kills the prey in order extract nutrients from it and use it to benefit itself, and it does so using specialized adaptations specific for that purpose and not just accidentally (like a broken tree branch falling down killing somebody down below doesn't make the tree carnivorous)

So a carnivorous plant needs to have ALL of these traits:

1. capturing or trapping prey in specialized, usually attractive, traps;
2. killing the captured prey;
3. digesting the prey;
4. absorption of metabolites (nutrients) from the killed and digested prey;
5. use of these metabolites for plant growth and development.

...in order to be considered a carnivorous plant.

Source: Carnivorous Plants: Physiology, Ecology, and Evolution from Oxford University Press

(HIGHLY recommend if you're interested in this topic, it's an extremely good book and the best comprehensive overview on carnivorous plants at the moment, with fairly up to date information from this rapidly developing field of study!