The detectives can't ask any more questions until a lawyer is present. So the lead detective doesn't talk to him at all but just stares at him. For hours. He doesn't say one word but sits in the room. The killer couldn't take the silence anymore and confessed. All he did was look at him.
Guys want to tell what they did and just being nice/professional and listening to them
There are two great examples of coercion. Nothing was violated in either of them. The list goes on and on. The list is long and NO Rights are violated. Sometimes just presence can be used a coercion tool.
The time-honored "good cop bad cop" routine, in which one detective browbeats the suspect and the other pretends to be looking out for him. People tend to trust and talk to someone they perceive as their protector.
Another basic technique is maximization, in which the police try to scare the suspect into talking by telling him all of the horrible things he'll face if he's convicted of the crime in a court of law.
Again, nary a Right is violated.