I couldn't find this question on the forums, so I apologize if this has already been asked... but what purpose does the Bonus Bar serve? I can't figure out what it does! LOL!
The % on the bonus bar increases when you search a square with more evidence (e.g. blood) or when you find a piece of evidence that can be tested.
Although it may not seem like much, the increase in % gives you more XP for each square that you search.
For example, say searching a normal square gives you 10XP; if your bonus bar is at 100% then you get 100% more XP, which equals 20XP