they get tons of media requests and don't want or need to be doing them all. As their spokesperson, he goes on the interviews and says what the family is feeling.

This protects them from getting ambushed by bullshit questions and having to react quickly and effectively on national TV, especially since they are not trained media professionals.

Additionally, it spares the family from having to constantly publicly relive the tragedy. He serves as a buffer who can help them keep the case from fading out of the spotlight, and answer questions in a professional, prepared, and measured manner.