Matthew's stepfather, "Dateline's" Keith Morrison, his mom, Suzanne Morrison, along with 3 of his sisters, sat down with "Today's" Savannah Guthrie to reveal what they believe were critical factors in Matthew's death.

Madeline, one of Matthew's sisters, made the point that Matthew might not have even been aware he had relapsed. He was coming off a stretch of sobriety during and after his book tour, and was taking ketamine for therapeutic purposes. Perry then started getting ketamine on the black market and was taking massive doses on his own.

The family talked about Matthew being headstrong, with a will of his own, and also how he was fundamentally a lonely person who was struggling.

As we extensively reported, 5 people -- including 2 doctors -- were charged in Perry's death. Three have pled guilty. One of the doctors and the "Ketamine Queen" have pled not guilty.

Keith said he was thrilled to see accountability, and made the point -- if you supply an addict drugs and he dies, "You're going down, baby."