Police in Omaha, Neb., are investigating the possibility of a connection between the murders of a university professor and his wife and two other local homicides.

Roger and Mary Brumback, both aged 65, were killed in their home on Tuesday, CNN reports. Their bodies were discovered by police officers who were investigating a welfare call.

So far, police have been unwilling to reveal much information about the Brumback case, in an attempt to preserve the integrity of their investigation, CNN reports. However, they have stated that a cold case unit has been called in to explore a possible link between the homicides and the unsolved deaths of Thomas Hunter and Shirlee Sherman.

CNN affiliate KETV reports that Hunter, 11, and Sherman, his family’s housekeeper, were slain in March 2008. Several years later, police have still not identified their assailant.

"When I heard the news last night, I was literally shaken -- literally," Laura Neece-Baltaro, a friend of the Brumbacks, told KETV. She had known the deceased couple since 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 added. "It's a terrible loss to the whole world that they're no longer with us."

Roger Brumback had been a professor at Creighton University. According to the institution’s website, the husband attended Pennsylvania State University and taught in Creighton’s pathology and neurology departments.

"It's just kind of shocking to have somebody that seemed so full of life and invincible taken so suddenly," Creighton medical student Justin McCarthy told KETV. According to CNN, a prayer service for the Brumbacks was held at Creighton on Thursday.