By Gan Matthews, NEWS 9

The parents of 22-year-old Chad Robinson spoke out Friday about how the perils of drug abuse addiction can devastate a family. Chad Robinson attacked his grandparents with a knife last summer.

Chad Robinson's parents said although they tried to help him, his addiction grew worse.

"As it progressed, he got into coke, eventually heroine, and towards the end we discovered he was doing crack," Greg Robinson said.

"I kept waiting for the police to tell me my son was dead," Londa Robinson said.

Last July, the Robinsons got a call telling them that their son was under the influence of drugs and had assaulted his grandparents.

Chad Robinson had repeatedly stabbed Connie and Mary Hornbuckle as they slept. Although the couple lost a life-threatening amount of blood, they survived the attack.

"I just knew it couldn't have been Chad," Londa Robinson said.

The investigators determined Chad Robinson was indeed the killer, and now his parents have a message for parents.

"If you like in your gut, if you have one thought, one inkling in your mind, drug test them. You don't have to be their best friends, but you have to save their lives," Londa Robinson said.

"These drugs today are nothing like they were when I was a teenager, and parents need to take it seriously. The risks are so much greater now," Greg Robinson said.

Last week, Londa Robinson got a Mother's Day card from Chad. It was the first Mother's Day card she's received from her son in five years.