This is how DI Bullet thinks the crime happened:

A silver Audi, number plate NG58 VXW, screeches round a corner and into the street.Four men jump out and start firing shotguns. The driver is in charge and calls orders to the others.The men are dressed in camouflage with dark jackets. Two men are masked.The masked men hold guns on two security guards, while an unmasked man tackles one to the ground and cuts the chain attaching a case to the guard's arm.While this is happening, the driver approaches Seth, Lila and Liz, threatens them with a shotgun and drags Liz back to the car and pushes her inside.The four men then jump into the car which pulls away at speed.The car is abandoned a few miles away with Liz still inside.The unmasked robber is short (approx. 5 feet 3 inches), of Indian ethnicity, in his early 20s, overweight and has long, dark hair.The driver is tall (approx. 6 feet 4 inches), Caucasian, bald and has a muscley build.

The unmasked robber is the man known as Fat Baz. The evidence for this is:

the description from both witnesses matches him very closelythe Photofit is a very good resemblance of himboth witnesses identified him in an identity parade.

The driver is the man known as The Sergeant. The evidence for this is:

the description from both witnesses matches him very closelythe Photofit is a very good resemblance of himboth witnesses identified him in an identity parade.

The case for the prosecution

The men known as The Sergeant and Fat Baz maintain that they are innocent of the crime of which they are accused during their interviews with DI Bullet and both plead not guilty at court.

The alibi offered by both men is not believed, as the only people that can verify where the two were at the time of the crime have prior criminal records.

The prosecution offer the following evidence:

statements taken from both witnessesrecordings of the interviews with both witnessesthe outcome of the identification procedures attended by both witnessesthe Photofits are not entered as evidence, but mention of their similarity to the two people accused is made in the opening statement of the prosecuting barrister.

This evidence is offered in support of the conclusions drawn by DI Bullet and of the guilt of the men known as The Sergeant and Fat Baz.

The case for the defence

The defence team have hired you as an expert psychologist and asked you to work through the prosecution defence and report any problems you can see. Below are the key pieces of evidence being used by the prosecution.

Think about each one carefully in light of all you have learned about the psychology of eyewitnesses and police investigations. Is the evidence sound?

The initial statements provided by the two eyewitnesses are consistent in terms of describing what happenedThe interviews with both eyewitnesses provide detailed descriptions that are a very good match for the two men accusedSeveral members of the public identified the accused from the PhotofitsBoth eyewitnesses identified the two men accused in line-ups.

Summing up DI Bullet's case

How easy was it to evaluate the evidence, and did your evaluation match that of the expert? Although the evidence is consistent and may appear persuasive in suggesting the guilt of The Sergeant and Fat Baz, there were significant flaws throughout the entire investigation. In particular:

We would expect the statements to be consistent because of the co-witnessing effect. The witnesses heard each other's account, which could easily have led them to change their memories to fit what they heard the other witness say.The interviews were based on a very large number of leading questions that introduced a lot of post-event information. Again, this could easily result in the memories of the witnesses changing to incorporate the information supplied in the questions.The composites were created using a system that is not a good match for how we remember and recognise faces. The images produced are therefore unlikely to be accurate.The identification parades involved a simultaneous presentation and both witnesses were given instructions that would have led them to believe that the perpetrator was present. In addition, they were actively encouraged to select someone.

There is also the fact that the only evidence available was that of eyewitness testimony – which is not really reliable enough to build a case on in the absence of other evidence. It is also important to consider the overall approach to the investigation. DI Bullet had a hunch as to who the perpetrators were following the initial statements. He then conducted the rest of the investigation in order to produce evidence that the two men were guilty, including asking leading questions that conformed to his idea of how the crime unfolded and who committed it.

DS Sund solves the crime

It should be clear by now that DS Sund conducted her investigation using a very different approach to DI Bullet, and that the techniques she used were based on psychological knowledge of eyewitness memory. Will you be able to find problems in the way she handled things or will her investigation stand up to your expert scrutiny?

DS Sund is not confident that she has an accurate description of the crime, but based on the evidence she gained from the witnesses, the following is her best estimate of how the crime happened:

Seth, Lila and Liz enter the street just as two armed men approach a security van.One man is masked, and the other is not, though may initially be wearing a helmet that is knocked off in a fight with one of the guards.The unmasked robber struggles with one of the guards, pushes him to the ground and removes a case that is chained to the guard using some form of tool.While this is happening, a third man approaches the witnesses as Liz has taken out a mobile phone. This man is likely to be masked, either like the other man or possibly wearing a cap and sunglasses.As the man grabs Liz, a silver Audi, number plate NG58 VXW, reverses into the street and all four doors open. The driver gets out and the other three men run towards the car and get in. The one near the witnesses drags Liz with him and forces her into the car, which then drives away.The men were wearing dark jackets, possibly with hoods, and army fatigues.The unmasked robber is 5 feet 9 inches, in his early 20s, of average build, possibly slim, and has dark hair, darkish skin and is of either Middle Eastern or Indian ethnicity.The driver is also about 5 feet 9 inches, Caucasian, in his 30s, has short hair and had a muscley build.

The unmasked robber is the man shown in the right-hand image above. The evidence for this is:

The description from the witnesses does not contain any details that would rule him outOne of the witnesses identified him in an identity parade.

The driver is the man shown in the left-hand image above. The evidence for this is:

The description from the witnesses does not contain any details that would rule him outOne of the witnesses identified him in an identity parade.

The case for the prosecution

During their interviews with DS Sund, the two men maintain that they are innocent of the crime of which they are accused and both plead not guilty at court. Neither are able to offer an alibi that can be substantiated. The prosecution offer the following evidence:

statements taken from both witnessesrecordings of the interviews with both witnessesthe outcome of the identification procedures attended by both witnesses.

This evidence is offered in support of the conclusions drawn by DS Sund and of the guilt of the two men.

© The Open University/iStockphoto.com/jawphotos

The case for the defence

The defence team have hired you as an expert psychologist and asked you to work through the prosecution defence and report any problems you can see. Below are the key pieces of evidence being used by the prosecution.

Think about each one carefully in light of all you have learned about the psychology of eyewitnesses and police investigations. Is the evidence sound?

The initial statements provided by the two eyewitnesses are very consistent in terms of describing what happened.The interviews with both eyewitnesses provide detailed descriptions that are a very good match for the two men accused.The two men were identified by one of the eyewitnesses.

As you did with DI Bullet's case, in the next step you will test your evaluation of the evidence obtained by DS Sund by completing a quiz. Each question in the quiz contains one of the pieces of evidence above and several potential ways of evaluating it. One of these evaluations was provided by a psychological expert on eyewitness testimony that has acted as an expert witness in court. See if your evaluation matches theirs.

Summing up DS Sund's case

How easy was it to evaluate the evidence and the way it was collected, and did your evaluation match that of the expert?

As with DI Bullet's investigation, there is the fact that the only evidence available was that of eyewitness testimony – which is not really reliable enough to build a case on in the absence of other evidence. However, unlike DI Bullet, DS Sund did attempt to evaluate the evidence objectively and test her ideas about what happened by looking for evidence that would disprove her hypotheses and rule people out of the investigation. In other words, she did not only look for evidence that was consistent with her ideas.

Two problems that you might have identified were:

there were inconsistencies in the testimonies of the witnessesonly one of the witnesses identified each of the suspects.

Although these points are worth considering, the question to ask is whether it is better to have one unbiased identification than two identifications from biased procedures. In addition, we should be suspicious not of two witnesses who disagree on certain details, but of witnesses who offer almost identical accounts – as the chances are this is either because of the co-witnessing effect or poor investigative techniques (such as the use of leading questions).

However, how much weight you place on the two investigations and the evidence gathered is entirely up to you.

© The Open University