You basically have two available avenues.
- Become a police officer, and work your way into the position. Keep in mind that in smaller agencies you may have better opportunities than in larger agencies, but the pay/benefits may not be as good.
- Apply for civilian evidence tech positions. Please see these crime scene (and other investigative) positions in San Antonio. All of them are civilian, non-police jobs except the ones titled "police. . . ." They receive continuing training throughout their careers.
notice that all except the entry level position require an IAI certification. A full-time college student can join the IAI for $45 a year. https://www.memberleap.com/members/newmem/newmem1.php?mid=3654219599&lid=3223312&sf=A
hope this helps!