More and more agencies are looking for people with a hard science degree. But there are some agencies that will accept a criminal justice degree. Best thing to do is check with the agencies you think you would like to work for and find out.
Also, there are over 250 jobs listed in the employment opportunity page of the Crime Scene Investigator Network. Many are entry level jobs. Look through the job announcements to see what employers require.
Ashik Azim wrote
Can you just get a degree in Criminal Justice to become a Criminal Scene Investigator or do you need a degree in science?