Murder-Suicide Case: Jimmie Johnson's Mother-in-Law 'Snapped' After Battling Depression Over Late Son's Freak Skydiving Accident

NASCAR legend Jimmie Johnson's nephew said he believed that his grandmother Terry Janway "snapped" and lost control after battling depression over her late son's freak skydiving accident, RadarOnline.com has learned.

Police in Muskogee, Oklahoma, said that Terry is the prime suspect after she was found dead in her home along with her husband, Jack, and their 11-year-old grandson Dalton, who resided with them since the age of two. Investigators believe Terry fatally shot her husband and grandson before turning the weapon on herself.

Terry and Jack were the parents of his wife, Chandra, who the pro driver has been married to since 2004.

The shocking deaths of his in-laws and young Dalton are being investigated as a murder-suicide, leading Johnson to pull out of his upcoming NASCAR Cup Series race.

Terry and Jack's older grandson, Seth Robison, 16, who is the half-brother of Dalton, shared that his grandmother had been struggling with long-term depression stemming from the sudden and traumatic loss of her beloved 27-year-old son, Jordan.

"My grandmother, she was a very sweet lady. If you met her she was the nicest person you ever met in your life," Seth told Daily Mail. "And I guess unknown to me, and quite a lot of other people, she had been struggling with depression and stuff we didn't know about until it was too late."

"About nine years ago my grandparents lost their son – my uncle – in a skydiving accident, and I now believe that's what started her descent into depression."

As RadarOnline.com reported, Jordan was killed in a 2014 skydiving accident after colliding with another skilled jumper while practicing a maneuver. He was knocked unconscious mid-air, leaving him unable to open his parachute.

The owner of Skydive San Diego said they have chips that automatically deploy in the case of an emergency, but it was undergoing maintenance at the time. Jordan was not required to jump with one as he was a seasoned skydiver doing more than 1,000 jumps.

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"I was the one that had to break the news to my aunt Channie," Seth shared about the latest tragedy to strike the family.

"She took it pretty hard, but I think she held herself together pretty well. But she was just in shock, she didn't believe it, she didn't want to believe it. I didn't either."