BSc Forensic Science is a three years undergraduate degree. The eligibility criteria vary from one college to other. But the minimum eligibility is that the candidate must have passed 10+2 or equivalent from a recognized board with at least 50% marks in aggregate in physics, Chemistry, Maths and/or Biology as main subjects.
Some colleges offer admission on the basis of marks obtained in 12. Also some colleges conduct their own admission test. It depends on which college you choose.