Most of the reputed colleges conduct exam. The basic criteria of eligibility is (10+2) or equivalent qualification with Physics, Chemistry and Biology and/ or Math as main subjects and a min score of 55%. Admission In reputed institutes is usually through entrance exam whereas in other institutes you can take direct admission. I am enlisting a few good colleges which are doing really well in this field and are known for their quality education and better placements. Top colleges are:

Gujarat Forensic Sciences University, All India Institute of Medical Sciences
Lok Nayak Jayaprakash Narayan National Institute of Criminology & Forensic Science, 
Lovely Professional University Jalandhar, 
Jawaharlal Nehru Medical College, 
Dr Bhim Rao Ambedkar University Agra, 
IFS Nagpur, Pune, Aurangabad, 
Osmania University Hyderabad.