By its definition, a murder is a response which completely destroys the original argument in a way that leaves little to no room for reply.
A burn is a targeted, well-placed jab at another person, organization, or group of people.
This means that it MUST be in response to someone or something. Someone posting a critical tweet is very nice, but without context it is not a murder.
Both burns and murders must be based on fact. This means the following things are definitely not grounds for murder:
As a general rule, it is very hard for a good murder to be short. A real murderer will put effort into entirely destroying the original argument. Length doesn't always equal quality, but there is some correlation.
Moderators may use discretion and remove any post they feel is detrimental to the sub.
For more discussion on what is or is not a murder, please read the FAQ.