(CNN) -- A Pennsylvania prosecutor said Monday he will pursue the death penalty against a man charged over the weekend with a quadruple slaying in Northampton County.
"This is a capital case," Northampton County District Attorney John Morganelli said in a telephone interview. "He's a killer that needs to be put down."
Michael Eric Ballard, 36, was charged Sunday with four counts of murder for Saturday's killings in Northampton, about six miles north of Allentown and 50 miles north of Philadelphia.
A neighbor alerted police Saturday afternoon to a disturbance at the house where Denise Merhi, 39, lived with her father, Dennis Marsh, 62, and her grandfather, Alvin Marsh, 87, Morganelli said.
Inside, police found the bodies of the three relatives as well as that of a neighbor, 53-year-old Steven Zernhelt, Morganelli said.
Morganelli described Zernhelt as a "Good Samaritan looking to assist the other victims."
"He yelled over to his wife, 'Call 911;' he went in and he never came out," Morganelli said.
All four had been fatally stabbed; the elder Marsh's body was found in a wheelchair facing a television, a knife wound to the neck; Merhi's body was in the kitchen; the younger Marsh's body was in the basement; Zernhelt's body was just inside the front door, Morganelli said.
About a mile away from where police were investigating the grisly scene, an off-duty state trooper witnessed Ballard lose control of the vehicle he was driving -- which belonged to Merhi -- and wreck, Morganelli said.
When the trooper approached the vehicle, he saw Ballard covered in blood and asked him to explain, Morganelli said.
"It's obvious -- I just killed everyone," Ballard told the officer, Morganelli said. "I just killed four people."
Ballard was taken to St. Luke's Hospital in Allentown for treatment of what appeared to be knife injuries to his legs, Morganelli said.
"He'll be all right, unfortunately," Morganelli said.
Once Ballard is discharged, he will be sent to Northampton County Prison, Morganelli said.
Though a motive was not immediately apparent, "there was some relationship" between Ballard and Merhi, who had two children and worked as a phlebotomist, Morganelli said.
Ballard had been on parole -- living in a halfway house in Allentown -- since April, when he was released from prison. He had served approximately 15 years of a 20-year sentence for third-degree murder in neighboring Lehigh County, though it was not clear whether his release was for that crime.
Ballard had pleaded guilty to fatally stabbing a man in 1990, Morganelli said. "He was a career criminal," he added.
Merhi's children were with a grandmother at the Jersey Shore, Morganelli said.
The weapon in Saturday's killings is being sought, he said.