Great care must be taken when interrogating a suspect that the interrogator not promise what is illegal or not possible. Often the way to get an offender to talk is to offer to hear "his side of the story" or allow the offender to "straighten out the errors" in the current version of events. When the offender has given enough detail or the investigator has enough proof from other sources, then it becomes appropriate to make an accusation of guilt. Proof must be solid enough to convince the offender that the interrogator does know the whole story or at least enough to convict the offender. Accusations made too soon may backfire and close off the avenue of questioning the offender.
It can be difficult during the interrogation process to know exactly when to accuse the person being questioned of committing a crime. It is really a matter of each individual doing the interrogation to determine the "right" moment. There are definitely pitfalls. If an interrogator asks too early, the suspect is likely to deny his involvement. Then again, if the questioning goes on too long before an accusation is made, the suspect may have had enough time to steel him-or-herself, and will deny in this case as well. The interrogator has to have a sense that the suspect is on the verge of confessing. He or she must "test the waters" by employing techniques like "soft" accusations and keen observations of behavioral shifts and ask when that right moment appears.