For communication to be effective, including within the context of investigative interviews and criminal interrogations, it is important to use the principle of synchrony, which is matching the individual's behavior and trying to synchronize, or simply be in sync with them. This can encompass many aspects of behavior such as hand and body movements during communication, position of the body in general, legs or arms crosses or not, interlacing fingers, leaning a certain way, etc. We can also match their tone while speaking as well as their word use, breathing rate and even blinking rate. Another factor to consider is matching their dress and appearance, so for instance if you are interviewing a street-gang member, it may be beneficial to drop the suit and dress down in much more relaxed clothing. The same is true when interviewing a CEO on a corporate embezzlement case, you would not want to wear a tee shirt and jeans in the interview. The more similar we appear to the person we are talking with, the more likely we will gain their trust, cooperation and build rapport.
Recent research was conducted that focused on convergence of speech rate during communication between people and how it improved cooperation between them. What this research showed was that when communication partners spoke at the same rate, their cooperation with one another increased. This adds support for one other aspect of the principle of synchrony, or as it's sometimes called "matching & mirroring" or "behavioral mimicry", among others. Quite simply this principle reinforces the idea that people like and trust people who are like them, which is a critical component of conducting investigative interviews and criminal interrogations.
One cautionary note before you go out and copy everything about everybody when you talk with them. This is a natural process and outcome during communication when rapport develops and trust is in place between the conversation partners. People naturally become in sync and the conversation flows smoothly and communication is more effective. Our goal in training people is to develop their awareness of this and increase their understanding of how their behavior may positively or negatively affect the outcome of an interview or interrogation. The cautionary note is this; if matching and mirroring is done in an obvious or blatant manner it can come across as insincere and manipulative and have the opposite of the intended outcome, whereby negatively impacting trust and rapport and reducing cooperation. These techniques need to be below the conscious radar of the person and it needs to be done in a manner to facilitate communication and not to manipulate the individual.