Surprise your suspect for more effective interviews
Many investigators give up the valuable element of surprise by contacting potential suspects by telephone
Getting to the truth is the goal of any law enforcement investigation. Gathering statements from potential suspects plays an important role in furthering that goal. However, these interviews can prove challenging because many times the offender has the opposite goal as getting to the truth could result in them being criminally charged.
The added pressure for investigators is that in some cases, successful prosecution of crimes such as child sexual abuse can hinge on statements made by the offender. This makes it imperative that officers are as effective in their suspect interviews as possible. Taking the extra time to locate your suspect in the field and catch them off guard can increase your chances of a successful interview.
Surprise interviews are advantageous in three main ways:
1. IT’S TOUGH TO LIE ON THE SPOT
Several studies by Dr. Aldert Vrij at the University of Portsmouth have supported what many cops experience on the streets: lying is far more challenging for people than telling the truth. When a person is telling the truth, they simply repeat what happened from memory. But when we attempt to deceive someone, we must take on several additional cognitive challenges.
We first have to invent the lie. Then we have to think of enough details to help ensure that the lie is believed. Next, we have to evaluate those lies to ensure that they don’t contradict any potential evidence out there. The challenge for the liar is that if they don’t give enough details, he or she won’t be believed. On the other hand, if the liar says too much, they run the risk of lying about details that can later be verified as false, thus exposing the entire story as fabricated. On top of all that, the liar then has to role-play what they think the appropriate emotions and body movements should be to match their chosen lie to further enhance their attempted credibility. 
Surprising the offender forces them to do all of that on the spot. Added distractions such as being confronted by the police in public and/or the possibility of arrest help to increase the cognitive pressure they experience. While they are trying to sort out what is happening to them, you will be asking basic questions about your case. Trying to speak intelligently while your brain is multitasking is just plain hard for most people. Increasing cognitive pressure on the person you are interviewing increases your chances of recognizing any deception on the part of the offender because it will help to magnify any verbal or physical tells present in that individual as they attempt to sell you on their lie. 
One way the liar can mitigate some of the above problems is by preparing for the interview ahead of time. The liar can do this by reviewing their knowledge of the crime to help anticipate any questions investigators may ask so that the liar can attempt to answer those questions accordingly. The more questions anticipated, the more questions the liar can give a well thought out answer to. With enough planning and preparation, the liar can greatly reduce the number of deceptive cues they give off because they are under less stress answering the questions because of the earlier preparation.
Studies into deception suggest that if given the opportunity, liars will attempt to anticipate the investigator's questions.  Like an actor preparing to play a part, the more time they have to practice, the better they will perform under pressure. The better they perform, the more difficult it will be for the investigator to discern deceptive from truthful statements. With enough time and forethought, the liar may also be able to anticipate and explain away evidence confronting them that would otherwise have incriminated them further.
The goal then for the investigator attempting to detect any deception would be to ask unanticipated questions.  Unanticipated questions force the suspect to answer tough questions on the spot with little time to consider the ramifications of their statements. The liar is then forced to decide on what to say next. If they choose the easy route by responding with a simple “I don’t know” or “I don’t remember,” they run the risk that too many of these responses will cast suspicion on their entire story. If they do choose to answer the questions, the chances of mistakes greatly increase but they haven’t had time to think of how their new lie affects their previous lies. With surprise interviews, an entire encounter is an unanticipated event, forcing the suspect into lying off the top of their head.
2. INCREASE YOUR CHANCE OF GETTING A STATEMENT
Police stations can be intimidating places for many people. Scheduling your interview allows time for a subject's mind to run wild with imagined police brutality in the interrogation room. By surprising the offender in public and choosing your words wisely, you can lower the person's guard simply by presenting yourself as a friendly fact-finder who wants to hear their side of the story.
Asking for a consensual interview face to face encourages participation because it’s difficult for most people to ignore someone in person who is asking politely. This is true even for people who engage in criminal activity. Investigators can exploit this tendency by confronting suspects in public places where they are forced to say no to your face or flee to avoid questioning. You have also avoided the issue of them being in custody since you asked them to voluntarily speak with you in a public place.
Even if the suspect proceeds to lie through their teeth, you have gotten a statement from them and any statement from the suspect is better than no statement from the suspect. If they do attempt to flee, that’s a pretty good indicator they’re afraid to talk about the issue at hand and still better than nothing.
The other advantage the investigator has in this scenario is that the offender must consider how his or her response will look to the officer or any bystanders that may be in the area. In my current duties, I investigate a lot of sex crimes. On top of the possible criminal penalties, these can be extremely embarrassing crimes to have committed and many times the offender and victim are acquainted somehow. Often the offender is aware of the allegations but not the status of the investigation. If they’ve told their family and friends that they’ve done nothing wrong, it becomes very difficult to slam the door in your face or refuse to talk while maintaining proclaimed innocence in front of these people.
Another problem with telephoning suspects to schedule interviews is that it gives the offender too many choices and too much time to evaluate those choices. If I call you to request an interview, once the phone call ends, you can then evaluate what was said and think through what your next step should be.
If your offender is guilty of the crime under investigation, nothing good is going to happen for the investigation at this time. The offender may choose to simply ignore your request and leave you hanging. The offender may contact an attorney who certainly won’t advise their client that making a full confession is in their best interest. In a best-case scenario, the offender will have ample time to formulate and rehearse their statement before the interview that will make it that much harder for you to pick up on any deceptions.
3. UNCOVER ADDITIONAL EVIDENCE
A good rule of thumb for any investigation is that you don’t know what you don’t know. Every good street cop learns that anything can happen when you start conducting stops, i.e., the broken taillight traffic stop that leads to an arrest with narcotics and guns being seized. Surprising your offender in public applies the same logic to your interviews.
For example, a few years back, my partner was assigned to investigate a sexual abuse case involving a local teacher and one of his students. We went to the high school where we were told the teacher had left early for the day. We then went to his apartment and knocked on his door in hopes of interviewing him. As we identified ourselves and explained our reason for being there, he immediately started sweating and stumbling over his words. An interview with two police detectives about a possible sexual relationship with one of his students was not on his afternoon agenda. In this scenario, our mere presence had put him into cognitive overload attempting to process what was happening.
Further helping our case was that the apartment layout was such that when the front door opened, I was able to see down the hallway and into his bedroom. As my partner continued to ask him questions, I kept my eye on any potential threats inside the apartment. His bad luck continued when I spotted the female student sticking her head out of his bedroom to see what was going on. This observation allowed us to obtain a search warrant for the residence which led to further evidence of his guilt within the apartment. This was evidence that we not previously known existed or would have otherwise not been able to collect.
We were later able to testify at trial that the victim had been in the offender’s bedroom upon our arrival, which certainly helped to support the prosecutor’s assertion that they had an inappropriate sexual relationship. The offender would not have invited us over to view the victim in his bedroom had we scheduled the interview with him over the phone.
Like a lot of things in police work, a little bit of good luck always helps. But it’s a very rare offender who schedules an appointment with the detective and brings evidence of their guilt with them to help the investigation. Drugs, stolen goods, weapons and child pornography are all things the suspect would rather keep from you if given the chance.
Finally, any officer safety and/or tactical concerns should always take precedence and officers should never put themselves in an unsafe situation. That being said, by taking advantage of surprise interviews you’ll find that the additional cognitive load applied to the suspect will lead to more success in your interviews. And you may just put yourself in a position to be in the right place at the right time when it comes to uncovering additional evidence.
1. Vrij A, Granhag P, Mann S, Leal S. Outsmarting the liars: Toward a cognitive lie detection approach. Current Directions in Psychological Science, 2011, 20(1), 28-32.
3. Hartwig M, Anders GP, Strömwall L. Guilty and innocent suspects’ strategies during police interrogations. Psychology, Crime & Law, 2007, 13(2), pp.213-227.