These two terms are not ones I have used, but I do believe I can answer your question as I volunteer in a jail as an on-call crisis counselor. The introductory statement is simply a summary of what is currently undergoing investigation and what the people know about what happened. For example, the investigators of the bank robbery know that three people for sure were involved, that money was stolen, that someone drove the get-away car, and the bag which contained the money has been found, empty. This attempt is to get the person to fill in any of the blanks, to help the investigators which also may help the person being interviewed.
The participatory accusation is to have the same person be seated in the investigation room, maybe go through the same information, but to then accuse the person of participating in the bank robbery. Perhaps they have a witness who is willing to testify, or will make a deal at that point to get more information about who else was involved. The true difference is that this one accuses the interviewee of participating in the crime of bank robbing.
Both methods are used with one chosen according to the information and proof the investigators have accrued so far. Later in the interrogation, both methods may be used. For those who have not been through this process before, many are frightened, and often my call to visit a jailed person comes at this point.