Lets go back to Silence of the Lambs. In order for this method of capturing the killer to work you have to have a definite suspect. Then you have to shadow this person to see what he sees every day. This can take a considerable amount of time and include a number of people working on this part of the case. Chances are that you will work a long time until you can move in and catch him. Arthur Lee Allen was the favorite suspect of most of the detectives and was watched for a long time. This also usually is a 24 hour type of  watching and is a big operation. This, for example, is for only one person and you can see how the watching can expand for watching three or four or more people. In the meantime other crimes are