It amazes me how tunnel vision affects investigations. In criminal cases, I usually have the benefit of going in after the case has been investigated by the police. I can see what they did, and I can't see what they didn't do.
What amazes me is how tunnel vision almost takes over an investigation. It is like the investigators become possessed by something causing them to only focus on one suspect. While more often than not, they usually have the right suspect, by having tunnel vision they end up missing key evidence and testimony by others. Think of it this way, if you are looking at the possibility of other suspects, you are more likely to broaden your search for clues and evidence. When you do this, you are more likely to discover more evidence. This includes evidence against the given suspect.
When investigators focus on one suspect, they often allow other suspects to go free, They also narrow the search of evidence so small that some obvious evidence is over looked. I am not saying these are bad investigators. What I am saying is that investigators need to be aware of how tunnel vision can cause you to narrow your focus so much that you miss key evidence. This is a psychological thing that happens "naturally" and investigators need to fight the tendency to have tunnel vision.
Part of the problem is that investigators are pressured to clear cases by arrest, so once they get a suspect, they narrow the search of clues and evidence too quickly.
This was just something that hit me as I am working on a current case.
Whatever you do - Stay safe!