Out of the three potential topic areas you mentioned I would be tempted to do something related to eyewitness testimony as you will be able to access plenty of exisiting literature and background material, a great deal of which will be quantitative in nature e.g. experimental research.
To get some topic ideas have a look at the eyewitness information pages on the The forensic psychology website (see following links)
Hi, I'm a current third year psych student and I faced similar problems while thinking of topics for my final year project. In the end, I did a project on personality factors and attentional bias for emotive stimuli and conducted the experiment on fellow students so that it was more manageable (as opposed to the prison population).
I'm not too sure about criminal profiling and jury selection, but I think that you should be able to do something about eyewitness testimony if you are required to do some sort of empirical experiments. Try searching for past papers published in that area to get a feel of what has been done and what exactly you are interested in investigating. For example, I know that research on the effects of different types of questions on eyewitness testimony has been done on student populations.
