You can judge a person by what they are looking at on the internet. Though it is not conclusive, it certainly gives an indication of a persons interests and their mentality. For example, if someone was slices with a knife, and there was a recent search for that brand of knife and cutting procedures.. It can certainly be a good indication!
Past Internet searches clearly are indicative of an intent of some kind. Maybe the intent is to learn about a topic, however when that search topic matches a subsequent criminal act then it is more than a coincidence. An Internet search is the same as possessing a book, or having a conversation on a topic just before a crime is committed. It is all part of the evidence of a crime. Your Internet search history is, basically, your digital fingerprint. If it implicates a person in a crime, then its evidence, plain and simple.
A persons search history can definitely be a vital tool in order to provide evidence that a person had intent to commit a crime. For example searching for tips on how to make homemade bombs or how to adapt guns can be a big red flag. However, we must be careful and balance these with other evidence, as there is always the chance of a person merely satisfying curiosities without any malicious intent.
Usually when people make searches on the Internet they have a legit reason of why they are looking for that. If a person is looking up violent websites or even how to's that have to do with violence it can be assumed that the person is attempting to commit a violent crime. Of course there are other factors to consider. It may be a student doing a reasearch project or an Officer trying to find something to brush up their skills. Either way it can demonstrate intent to commit a crime but it cannot be the deciding factor to determine if in fact the person is doing such a thing.