Some things that law enforment officers do is seperate the witnesses as soon as possible so they do not have time to work up a story that they can all tell the police. Once seperated they are taken to an investigation room with 1-2 investigators inside the interrogation room and another 1-2 watching what is going in said room. This makes sure that more than one set of ears hear what is being said and more than one mind is at work piecing together parts of the story. This also lets the investigators to look at each eyewitness account in seperately and see which parts were the same and which parts were completely different. This is also a good technique as to seeing who is lying and who is telling the truth. As for legal rules, well there really aren't many that greatly affect the outcome of an eyewitness account or identification of, what I assume to be, the suspect. The only real law I can think of that would reduce some inaccuracy is giving that giving false information to the police is a crime itself and that you can also have the charge of interferring with an investigation by wasting the investigators time with a tall tale. Hope this helps.