Dennis Koula was a wealthy businessman who continued to go to work even though he earned enough to retire many times over. His wife, Merna, was a substitute teacher, and just like her husband, she loved to work. Then one day in May 2010, they failed to show up - because they were shot dead in their home.

The case shocked residents of La Crosse, Wis., where the Koulas were respected members of the COMMUNITY, seemingly loving parents to their grown children Eric and Cindy, and enthusiastic grandparents.

"It was an assassination," says John Christophersen, a former special agent with the Wisconsin Department of Justice, who investigated the case. "This is somebody that was lying in wait for them, prepared to execute them."

"Just didn't understand why, why they're like this at all. Such great people. You know, they're - now they're gone," Eric Koula says in an interview with 48 HOURS: "Desperate Measures," to be broadcast Saturday, Feb. 9 at 10:00 PM, ET/PT on the CBS Television Network.

"For my parents to die the way they did is just, it's the most bizarre twist of fate," says daughter Cindy Cowell. "For two people who were so against violence to be brutally shot, it just boggles the mind."

It was Eric who found his parents dead in their home. He tells 48 Hours he got worried when neither responded to calls. He headed to their home, where he found his father on the floor. His mother was slumped over her computer. Eric Koula called 911. But who would want the Koulas dead?

"There's nobody that stands out," Christophersen tells 48 HOURS.

The investigation would lead in many directions, including a tip from a neighbor - a banker - who tells police he had gotten death threats. And, as it turns out, a Google map search for his address, actually points to the Koula house.

Did the person threatening the neighbor get misled by the online maps, or were the Koulas killed by someone they knew?

Peter Van Sant and the 48 Hours team report on the investigation into the murders of Dennis and Merna Koula using interviews with family, friends, investigators and prosecutors. "48 HOURS: Desperate Measures" is produced by Susan Mallie. Amanda Cassandra is the associate producer. George Baluzy and Mead Stone are the producer editors. Marlon Disla is the editor. Anthony Batson is the senior broadcast producer. Susan Zirinsky is the senior executive producer.