Answer:
a deposition
Step-by-step explanation:
A deposition can be described as a witness who is used to gather information for the discovery of an event which occurred. A deposition can also be used for a trial under some circumstances. Usually, a deposition procedure starts with the swearing of a witness. If a deposition does not solve a case then it will most likely move to the court for trials.
Hence, the best discovery method they should use to gather information is through deposition.