Comment by dmbche

Sadly, events are far more complex than counting items. For example, during the Columbine shooting, many students thought there were 4 shooters (while there were only 2), because at some point one of them remove their hoodie and the other turned their baseball cap backwards. The police thought there were shooters on the second floor because of an optical illusion.

These types of problems are very widespread - it's not rare that people misremember details because of the stress and trauma, and it's also well known that the process of describing/asking questions can cause bias into the victim, as seen in the many cases of people admitting crimes they didn't commit after long interogations.

I've also heard that the quality of police sketches was highly related to the person making the sketch, some have high correlation rate but that is not the norm i.e.: the average sketch artist might not be reliable on average.

JCS Psychology on Youtube is a great channel showing the processes happening during interrogations, if you're interested.