Paul Ekman. "Telling Lies: Clues to Deceit in the Marketplace, Politics, and Marriage." 1995. New York: Norton.

Fritz Strack. "Inhibiting and Facilitating Conditions of the Human Smile: A Nonobstrusive Test of the Facial Feedback Hypothesis." Journal of Personality and Social Psychology. 1988. Vol. 54. No. 5. p. 768-777. Purchase here.

On the subject of facial expressions, a reader writes with this marvelous passage from the writings of Frederick Douglass, describing the inauguration of Abraham Lincoln:

"On this inauguration day, while waiting for the opening of the ceremonies, I made a discovery in regard to the Vice-President--Andrew Johnson. There are moments in the lives of most men, when the doors of their souls are open, and unconsciously to themselves, their true characters may be read by the observant eye. It was at such an instant I caught a glimpse of the real nature of this man, which all subsequent developments proved true. I was standing in the crowd by the side of Mrs. Thomas J. Dorsey, when Mr. Lincoln touched Mr. Johnson, and pointed me out to him. The first expression which came to his face, and which I think was the true index of his heart, was one of bitter contempt and aversion. Seeing that I observed him, he tried to assume a more friendly appearance; but it was too late; it was useless to close the door when all within had been seen. His first glance was the frown of the man, the second was the bland and sickly smile of the demagogue. I turned to Mrs. Dorsey and said, "Whatever Andrew Johnson may be, he certainly is no friend of our race."

The full passage is available here. Part II, chapter XII.

Klin has written a number of accounts of his research with "Who's Afraid of Virginia Woolf?" The most comprehensive is probably:

Ami Klin, Warren Jones, Robert Schultz, Fred Volkmar, and Donald Cohen. "Defining and Quantifying the Social Phenotype in Autism." American Journal of Psychiatry. 2002. Vol. 159. 895-908. Full article available here.

I would note that the effects of stress on perception--and the key role that experience plays in overcoming these kinds of effects--is by no means confined to police work. Here are the experiences of a reader, a physician named Jonathan Cohen, describing the same effect in medicine:

I am a neonatologist, a pediatrician who has specialized in the care of high risk and critically ill infants. I am very often handed a nearly lifeless infant following delivery. Early in my training, even the thought of going to any delivery in which pediatric assistance was likely to be needed (maybe 10% of all deliveries) would cause my pulse to soar and my body to "tighten". The reality of the situation is that most times, no action is required other than drying the baby and being patient. In only a few instances is true resuscitation required. Early on, I tended to over react (as most young and many grizzled pediatricians do) and as a result was overly aggressive. After the few events that required real action, I felt quite ill (even if the outcome was good). I spent a few years working on relaxation techniques and simple meditation in order to have the clarity necessary in these situations. By now, I have attended thousands of deliveries and performed hundreds of resuscitations on babies. The experience is diametrically the opposite of what I experienced a decade ago. I feel very much in control and have almost unbelievable clarity about these events.

For example, A few months ago, I was faced with a baby who required endotracheal intubation (a.k.a "a breathing tube"). In the process of placing the tube I noticed a small polyp on this infant's vocal cords. In this instance, I was in a loud and crowded delivery room and had been handed an infant whose heart was barely functioning. I was using a small laryngoscope to visualize an infant's airway which probably half a centimeter in diameter. I was probably 18 inches or so from my target. The polyp couldn't have been more than a quarter millimeter in size. I probably was directly visualizing this area for less than a half a second and during that interval I was concentrating on passing a tube through the cords rather than inspecting them. What I find fascinating is two fold. First, very often we perform examinations of infants vocal cords and upper airway that are elective in nature and therefore very calm a slow paced. The level of detail is such that what I saw in that moment during the resuscitation is often missed. Secondly, I had a full and accurate image of the entire picture in my mind, not just a "feeling" of something unusual. It was as if the baby's tiny vocal cords were blown up on a large poster board. When the infant was stable and we had time to perform a slow and thoughtful examination, the polyp was exactly as I imagined it, as were other sub-details of the infant's anatomy. I'm not sure at what point the experience of reviving a baby was altered from nerve wracking to manageable. By no means is it mundane. My pulse still quickens, but my energy is now very focused. As a result, I have become patient in the moment and have truly learned that it is usually better to "not just do something, but rather stand there." Following these moments, I have euphoria very similar to runners high and a senseof clarity that lasts for at least a few additional minutes if not hours.

B. Keith Payne, Alan J. Lambert, Larry L. Jacoby. "Best Laid Plans: Effects of Goals on Accessibility Bias and Cognitive Control in Race-Based Misperceptions of Weapons." Journal of Experimental Social Psychology. 2002. Vol. 38. p. 384-396. Purchase here.

Alan J. Lambert, B. Keith Payne, Larry L. Jacoby, Lara M. Shaffer, et al. "Stereotypes as Dominant Responses: On the 'Social Facilitation' of Prejudice in Anticipated Public Contexts." Journal of Personality and Social Psychology. 2003. Vol. 84. No. 2. p. 277-295. Purchase here.

Keith Payne, "Prejudice and Perception: The Role of Automatic and Controlled Processes in Misperceiving a Weapon." Journal of Personality and Social Psychology. 2001. Vol. 81. No. 2. p. 181-192. Purchase here.

See also:

Anthony Greenwald. "Targets of Discrimination: Effects of Race on responses to weapons holders." Journal of Experimental Social Psychology. 2003. Vol. 39. P. 399-405. Full text available here.

Joshua Correll, Bernadette Park, Charles Judd and Bernd Wittenbrink. "The Police Officer's Dilemma: Using Ethnicity to Disambiguate Potentially Hostile Individuals." Journal of Personality and Social Psychology. 2002. Vol. 83, 1314-1329. This study is actually a videogame, in which you see whites and blacks in ambiguous positions and have to decide whether to shoot or not. Try it. It's quite sobering. Available here.

Nancy L. Etcoff, Paul Ekman, et al "Lie Detection and Language Comprehension." Nature. Vol. 405. May 11, 2000. See article here.

Carlene Wilson. "Research on One-and Two-Person Patrols: Distinguishing Fact from Fiction." South Australia: Australasian Centre for Policing Research. 1991.

Scott H. Decker and Allen E. Wagner. "The Impact of Patrol Staffing on Police-Citizen Injuries and Dispositions." Journal of Criminal Justice. 1982. Vol. 10. p. 375-382.

Journal homepage.

And resources for abstracts, here.

An Israeli police officer by the name of Sam Schwartz emailed the following comment on the Diallo chapter, which I think is worth quoting in full. Schwartz begins by quoting the following paragraph from Blink:

"The officers, observing Diallo on the stoop, sized him up and in that instant decided he looked suspicious. That was mistake number one. Then they backed the car up, and Diallou didn't move. [Officer] Carroll later said that "amazed" him: How brazen was this man, who didn't run at the sight of the police? Diallou wasn't brazen. He was curious. That was mistake number two. Then Carroll and [officer] Murphy stepped toward Diallou on the stoop and watched him turn slightly to the side, and make a movement for his pocket. In that split second, they decided he was dangerous. But he was not. He was terrified. That was mistake number three."

Then he writes:

You use the word "mistake" to describe the behavior of the police officers at different stages of the incident and in general characterize the chain of events as a "mind-reading failure" and something between a tragic accident and a clear cut incident of racism.

I wanted to address the issue of whether the policemen made mistakes and how the string of mistakes constitutes a status of some kind of moral culpability on their part. The word "mistake" is defined as "an error or fault resulting from defective judgment, deficient knowledge, or carelessness" and in this sense, that does seem to be a fitting way of describing the officers' conduct here. However, I think the word mistake also carries the connotation that, were the situation to repeat itself, the person who made the mistake should behave differently. I don't know if that is the case here.

It is obvious that the officers where mistaken in their judgments that Amadou Diallo was a lookout for criminal activity, that he brazenly was challenging the police, and that when cornered he turned around to draw a weapon from his waistband. However, I don't think the officers were mistaken in their judgments that Diallou's standing on the stoop was suspicious, that his running from police who identified themselves verbally and with the presentation of their badges was suspect and that when he turned to draw an object from his right back quadrant, he was endangering their lives.

The essence of police patrol work is being able to spot people's behavior and objects which are out of the ordinary and that "don't fit." These are the ABCs which I try to teach all the officers in my unit. When you see someone standing in an unexpected place at an unexpected time, this raises your suspicions and it is elementary to go and question that person. When the officers saw Diallo on the stoop at that place and time, he was suspicious. He wasn't engaged in any criminal activity but he was suspicious and I think the police were correct in interviewing him.

On the other hand, I think that the Carroll's interpretation of Diallo's not running from them as "brazen" was a clear mistake and possibly motivated by prejudicial beliefs. The simplest algorithm for judging criminal behavior is that the guilty run and the innocent cooperate. The fact that Diallo stayed on the stoop should have been evidence of his innocence. If Diallo ran then the officers would most certainly have had their suspicions about him strengthened (and would have been correct in thinking so). This is eventually what happened when Diallo ran into the vestibule confirming the officers' belief that he was involved in criminal activity.

Conversely the fact that he didn't run and that this also confirmed the officers' suspicions about him, raises the question about the officers' presumptions of guilt based on extraneous considerations. If both A and not A lead to the same conclusion, then there's good reason to think the conclusion was fixed ahead of time. Their judgment on this issue indeed was mistaken and there is reason to think that it was not just an honest mistake. If I were inclined to give the officers the benefit of the doubt, I would investigate the possibility that Carroll's characterization of Diallo's behavior as brazen was not an intuition he actually felt at the time, but instead was something that he created after the incident, when reviewing the events, and trying to make sense of the fact that Diallo didn't run immediately. Carroll clearly said he had this intuition at the time, so such a hypothesis may be too generous to him. However, it's hard for me to explain his characterization if it was both not prejudicial and not retrospective.

Once the officers cornered Diallo in the vestibule and he turned to draw something out of his right rear waistband, I think the officers' decision to open fire was not mistaken. As you noted, in a dark vestibule at night, with adrenaline pumping, with a suspect who is in a strange place at a strange time, and who has already taken actions which confirm suspicions, the top of a wallet can appear remarkably like the slide of a gun. As you also noted, the time available to make a shoot-don't shoot decision here was infinitesimal. I don't think the police were wrong to decide to open fire.

It will probably never be possible to know what exactly was going on in the heads of the officers at the time. In this letter I focused on the issues you raised in your book but there are probably other relevant facts that either you didn't stress or that were never raised at the trial or in any public forum. It is also important to consider whether the officers followed NYPD guidelines regarding approaching a suspect and how/whether to engage in pursuit if the suspect flees. You correctly noted that such police procedures are often instituted in order to give the officers more time to make these life and death decisions. In this case, with more time to make the shoot-don't shoot decision, a different outcome might have prevailed. However, I am not sure what the NYPD guidelines are and I can think of a number of good reasons why the officers would have chosen to confront the suspect immediately and not allow him to escape into the vestibule.

In this light, I will confine myself in conclusion to restating the main points I hoped to convey in the letter. I think the officers were wrong to think that Diallo was brazen for not fleeing and this raises questions about their motivations. On the other hand, I think the police were right to think Diallo was suspicious in the first place, to believe that his running strengthened their suspicions, and to open fire when he reached behind him to grab a black, gun-sized object.

Schwartz's point has been reiterated by other police officers I have talked to since the book came out. They accept that the four officers in the case made a series of mistakes. But they think that I went too far in my criticism. Upon reflection, I accept the criticism. Schwartz, I believe, is quite right. My discussion of the shooting ought to have been more nuanced.