sorry to hear about what happened to your nephew but be assured that his life can be changed and transformed with jesus christ. i came out of gangs when i was 13 and did it with support and constant guidance from family and friends. i had protection but most of all, the desire to want to change. your 16 year old nephew will need knowledge about gangs and its consequences. i work in the juveniles inside the hall and trust me, most of them want to change but dont know how to get help and who to trust.
as for my case, i changed when i realized i had support and faith from others encouraging me to do more with my life. i had coaches who convinced me i was more than i could imagine.
so for your nephew, i would pour a tank of love onto him involving encouragement, discipline, knowledge, resources, counsel, and an ear for him to know you're listening and understand him.
instant change would be nice but the work you are doing on him will be imprints on his soul for life and he will remember it down the years. it took everything for me to change such as whoopings, my deep respect for my brothers, my true desire for sports and school, and the people in the backround who would always encourage me such as teachers, pastors, friends, family.
so ask about his goals, desires, future plans, and dreams. he may not know until someone asks and show they care for him to realize there is one. god bless and pete is in my prayers.