A wealthy hotel business owner and his wife were brutalized and stabbed to death in their million-dollar Rockville, Maryland home. The search for their killer would lead investigators halfway around the world and back.

A call for help after a savage attack. But who's responsible, and why?

On the morning of Mother's Day, Sunday, May 10, 2015, Katie and Andy Vilardo were waiting at a picnic area for their parents, Dick and Jody Vilardo, to celebrate the holiday. But their folks don't show up. Concerned, the kids rush to their parents' home in the upscale neighborhood of Rockville, Maryland.

Once inside, they call police, who are on scene within minutes of the 911 call. They follow the blood trail to the backyard.

"Her mother is on the floor with multiple catastrophic injuries, most notably to her neck. She is nearly decapitated," said John McCarthy, state's attorney for Montgomery County, Md.

Just outside the back patio door, another grim discovery.

"The father just a few feet away from the wife, collapsed on the patio, and he has multiple injuries, more than 40 stabbing injuries," said McCarthy. "They've obviously been deceased for some period of time."

Dick and Jody Vilardo's last contact with their kids was a phone call around 9 p.m. the night before. The couple spent the evening with friends at a nearby casino and returned home sometime after 11 p.m. But what horrific events occurred from Saturday night to Sunday morning? And who would want to kill Dick and Jody Vilardo?