Graduate vs Experienced Forensic Investigator

In an interview situation how are graduates supposed to compete with guys who already have x amount of years experience, especially in the Police Force environment?

You don't. Knowledge and experience are two different things and when someone is looking for experience, the only thing that you can do to "compete" when you don't have it is to demonstrate good judgement. That, unfortunately, is something not easily taught.

On the other hand, you have an advantage, I think, in terms of price. People with experience tend to want to be compensated for that which prices them out of some markets.

So, the simple answer is, look for positions that are more entry-level. Unless the economy really tanks, you won't find many experience people looking for these.

I think I have lost on a number of previous occasions due to this, I believe I have good answers for general forensic and competency framework questions but there are often answers that can be enhanced and expanded upon purely through your previous work experience - which I do not have.

This suggests that either you are looking at the wrong opportunities or your answers or style of answers are not as good as you think that they are. Interviewers don't simply look at the answers to their questions, they look at how you express yourself and what they can tell about your character, personality and ability to work on a team and independently.

You are assuming that it is about experience but it may be about something else. It might help to get some advice from someone objective who knows you like a former teacher. They may be more likely than we to be able to suggest what you might do, differently.

Also, the difference between knowledge and experience is not an "imbalance" it is a fact of life. Each has value but experience can only be acquired through time and practice. Accept that and look for opportunities to acquire it.

As Sean said, jobs with any level of seniority (i.e. Senior Associate vs Associate) are going to expect experience in the field. You need to focus on entry level jobs where they won't be expecting forensic knowledge and will instead focus on your general IT and problem solving skills and so you can equate some other type of problem solving that you have done and show how that is relevant to the issue that you are being asked to address.

Also, ask for feedback from you past interviews, or if you get a new interview that doesn't result in a job, ask them for feedback as soon as you get the notice (while it's still fresh and they may still remember). They may tell you about some issue which you are not aware of, and then you can refine your resume, or your answers, or develop some additional skill that rounds you out better as a candidate.