UPDATED 06/08/11 6:08 p.m.

MARENGO (CBS) — A man visiting his elderly parents was unable to save their lives Tuesday night when a neighbor with a history of mental problems attacked the couple with a knife inside their northwest suburban home. CBS 2′s Mike Puccinelli reports at the scene.

The son was able to fatally shoot the attacker after he also was stabbed, authorities said.

McHenry County Sheriff Keith Nygren described the killings in a quiet, semi-rural neighborhood off Coral Road and Route 20 in Marengo as “a random incident of violence.”

Police said Doran W. Bloom, 27, entered home of John “Jack” G. and Audrey Feldkamp in the 7500 block of Somerset Drive about 8:17 p.m. and fatally stabbed the couple. He also stabbed their son, Scott Feldkamp, who was visiting from Fort Myers, Fla..

Scott Feldkamp was able to retrieve a handgun from a bedroom and shoot Bloom, Nygren said Wednesday.

John Feldkamp, 83, and Bloom were pronounced dead at the scene. Audrey Feldkamp, 81, was flown by Flight for Life helicopter to St. Anthony’s Medical Center in Rockford, where she was pronounced dead, the victim of at least 14 stab wounds, the sheriff said.

Scott Feldkamp, 54, was transported by paramedics to Sherman Hospital in Elgin with several stab wounds not considered life-threatening. He was listed in fair condition Wednesday afternoon, according to hospital spokeswoman Christine Priester.

Nygren said investigators have pieced together events of the night based on Scott Feldkamp’s statements and evidence at the scene.

Scott Feldkamp said he saw his father being stabbed near the front door and attempted to stop the attack, but was stabbed himself. Scott Feldkamp then was able to make it to a second-floor bedroom where a 9 mm handgun was kept and shot Bloom in the family’s “great room.” Nygren said he believed Audrey Feldkamp was stabbed while Scott Feldkamp was going for the gun.

Nygren called the home invasion a random act of violence by a person with a history of mental health problems. There was no evidence of any connection between Bloom and the Feldkamp family, the sheriff said, adding that investigators have not been able to determine a motive for the attack.

Bloom’s parents have been cooperating with investigators, he said. Bloom’s mother said her son had moved into the family home in the 7700 block of Somerset, a quarter mile away from the Feldkamps, about a week ago. The estate homes in the neighborhood each sit on 3 to 5 acres of land.

Bloom had been living in the Woodstock area before then, Nygren said.

Bloom’s mother told police her son had had a history of mental health issues since high school, including “episodes of rage,” according to Nygren, who noted that Bloom had been receiving mental health treatment.

Authorities said Bloom also had a history of DUI arrests in Kane and McHenry counties.

Jack Feldkamp was well known in the Marengo area, said Peggie Stromberg, director of the Elgin Public Museum. “Jack had been around forever,” she said, adding that Feldkamp still went to work as a real estate agent every day.

“He was a wonderful broker. It is a tragic loss,” said Ellen Ritter, who worked with Feldkamp at Harmony Real Estate since 1994.

(Source: Sun-Times Media Wire © Chicago Sun-Times 2010. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)