The two youngest of their three children, Joseph, 13, and Anthony 10, "came home and couldn't get in the front door, and went to the back and saw blood on the back door. They got a neighbor with a key," said a source close to the investigation.
The couple had apparently engaged in a battle to the death with knives in nearly every room of the house, according to investigators, although the possibility of a murder-suicide had not been ruled out.
Police said they took three knives as evidence.
"The scene looked like a Quentin Tarantino movie," said a source familiar with the scene.
Blood was splattered everywhere "in most rooms of the house," said Sgt. Frank Hayes, head of the homicide investigation. The fight "appeared to start in the upstairs on the second floor."
Sophia DiAndrea was found in a blood-soaked rear bedroom while her husband was found in the front bedroom. Both had multiple stab wounds, he added.
Dr. Gary Collins, assistant medical examiner, performed autopsies, but the manner of death in both cases is pending.
"We don't know if it's a murder-suicide, or whether both contributed to the deaths," said Hayes. "We don't believe anyone else was involved."
Today, investigators and Collins will review everything, he added.
"We believe we know what led up to it," said Hayes, who acknowledged the couple had domestic problems.
"It's sensitive to the family and for the young kids," he added, saying he expected a "watered-down version" to be released.
A second source familiar with the investigation said the couple had been seeking a divorce.
Robert was a $44,860-a-year supervisor of water conveyance systems for the Water Department, hired on May 27, 1997, city records show.
Hired by the school district on Oct. 23, 1993, Sophia was a fifth-grade teacher who made $81,617 a year, school records show. She had worked four years at Anne Frank Elementary School, at 2000 Bowler St., an eight-minute ride away.
Co-workers of the couple did not return calls from the Daily News.
Last night, Fernando Gallard, a public-school spokesman, said that counselors would be provided today at the school for students and staff. A substitute teacher will take over DiAndrea's classroom.
"It's like we lost a member of the family," he added. "But we will try to have a normal school day."
The couple's two youngest children stayed with a relative on Saturday. Their oldest son, Robert Jr., 23, does not live at home, said a neighbor.
The DiAndreas bought their home for $138,000 on Jan. 31, 1997, city records show.
For years, children had been at the center of the couple's lives, said Laura Snyder, 47, a mother of two who lives across the street. "This was kids central."
Seven years ago, Snyder said, the couple started a Christmas pollyanna for all the kids in the neighborhood, and, four years ago, persuaded their parents to empty their garages of unused things for a streetwide yard sale.
The DiAndrea family were avid sports fans.
Robert was a "real football fanatic," said Snyder. He regularly threw footballs to his kids on the lawn and was a devout Eagles fan. His brown van, parked in the driveway yesterday, had an Eagles bumper sticker.
Sophia was "upbeat and laughing a lot," said Snyder.
Her late-model red Honda Accord, parked in front of their house, had a Phillies plate on the front bumper.
Their 13-year-old is "really into basketball," said Snyder.
The kids would perform skateboarding tricks and play baseball in the street, sometimes with tennis rackets instead of a bat, she added.
Yesterday, in a box outside the DiAndreas' front door, there was a Wiffle Ball bat, wrapped in tape, a baseball and an adult pair of athletic shoes.
Last fall, Robert took his sons to see a World Series game, Snyder said.
During summers, she added, the family often took camping trips in the Poconos, or rented a place for a week in Avalon, N.J. They took whitewater rafting trips down the Lehigh River.
"They were all-American boys and their dad was always with them," she said.
But Saturday, Snyder said, she heard "nothing" coming from the DiAndrea home.
"That's what was so shocking," she said.