Broadly, police-to-police co-operation is used to direct ongoing investigations to find the best and most efficient way to collect evidence in a way that it could be officially accepted in front of a court. Mutual (legal) assistance is the official exchange of information, where different legal procedures are followed to gather information, which then is subsequently used as evidence.
Generally, when the case reaches the threshold "reason to suspect that a criminal offence has been committed" and a criminal investigation shall be carried out, formal MLA procedures are applied. In other words, MLA instruments apply during the criminal investigation stage. Before that stage, instruments of police-to-police cooperation may apply.
Different types of information can be exchanged trough police-to-police cooperation, but the purpose needs to be clearly defined and information shall only be used for this defined purpose. In cases where coercive measures need to be applied to gather the requested information, police-to police cooperation is not possible.
