(CNN) -- Police in Omaha, Nebraska, said Thursday that they're looking into whether there's a connection between the recent killings of a university professor and his wife and two unsolved area homicides.
Roger and Mary Brumback, both 65, were found dead at their home early Tuesday by officers responding to a welfare call.
Police are saying little else about the case.
They do not plan to release additional information, police said, in order to protect the investigation, which is being led by a homicide unit.
However, they have said a cold case unit is assisting to determine whether there is a connection between the case and the unsolved killings of Shirlee Sherman and Thomas Hunter.
According to CNN affiliate KETV, 11-year-old Hunter and Sherman, the family's housekeeper, were killed in March 2008.
"When I heard the news last night, I was literally shaken -- literally," Laura Neece-Baltaro, a family friend of the Brumbacks, told KETV.
She met them when they all lived in Oklahoma in the 1990s.
"Why would anyone want to harm them? They did so much for the community here, and the community in Oklahoma City and they were still contributing. They still had a lot to give back," she said.
"It's a terrible loss to the whole world that they're no longer with us."
Roger Brumback was a professor at Creighton University.
According to the school's website, he attended Pennsylvania State University and worked in the pathology and neurology departments.
A prayer service was held at the school Thursday for the slain couple. Students wore white coats in tribute.
"It's just kind of shocking to have somebody that seemed so full of life and invincible taken so suddenly," said Creighton medical student Justin McCarthy, KETV reported.