"I can't imagine that it's easy for them," Berg said. "We spoke to a close family friend who gave us her insight on the family. They didn't want to participate in the film, but I can't imagine how difficult this must be for them. They thought this was a closed case and justice was served, and then all these questions continue to come up for 20 years. As the mother of a young girl who was murdered and had her life taken away, I'm sure that it's horrific for them," Berg said.

The Case Against Adnan Syed airs Sundays, 9 p.m. on HBO.