The three types of denial a suspect might use in an interrogation are simple denial, projection, and minimization.
In a simple denial, the suspect will deny involvement outright. “I didn’t do it.” This might mean the suspect really did not do it, or it might mean that he or she is lying. You need to watch body language. Does the person seem shocked? Nervous? Arrogant? Frustrated? Pleading? Grieving? While anyone can fake any emotion, looking carefully at simple cues will tell you if the suspect is telling the truth. Sometimes the suspect will simply say he knows nothing. You have to ask yourself if he knew about the crime, and does he know details that no one but the perpetrator would know? Try to trap him in a lie.
Minimization is when the suspects will admit some of what they did, but not other parts. “Yes, I robbed him, but I didn’t kill him!” Sometimes the suspect may claim self-defense, or suggest that the crime was no big deal and there was nothing wrong with it.
Projection involves blaming someone else. This is sometimes called the Twinkie defense. “Drugs made me do it.” “I was drunk.” “He or she was asking for it, and what else could I do?” “Violent video games made me do it.” “I had an abusive childhood.” “I was not in my right mind.” “I don’t remember.” This suspect might be establishing a defense strategy.