How post-event misinformation paradigm developed?
This is certainly pertinent to the work of Elizabeth Loftus and others. And Emily is completely correct in that how a witness is dealt with post-event can have profound and significant events on what they remember.
Loftus and Palmer named memory on their original paper as 'reconstructive' to indicate that memory is not a perfect record and can be edited either during the event itself or following the event.
Any number of factors can influence the memory during an event such as emotional state, what they are seeing and even the proximity of the criminal to other bystanders who can become linked within the mind of the witness.
Post-event, as Emily said is things like interviewing techniques that can heavily influence what the witness remembers. As Loftus and Palmer showed, even a very subtle change of words like 'smashed' or 'hit' can influence what the witness later reports themselves as seeing. That is the reason, the cognitive interview is the preferred option nowadays.
Also, memory is heavily influenced by temporal considerations and the memory may become degraded and more susceptible to change the longer the period between observation and report. Thus, interviews need to be carried out in haste.
You can ask leading questions or provide misinformation to help cause a false memory