Neighbours pointed towards the road outside the house and said that this was where the two boys used to play. It was at the quiet end of a quiet cul-de-sac. "But Mary never, ever left the door closed when they were out there," they said. "She supervised them at all times."
Yesterday, the road was a crime scene, cordoned-off by Garda tape. A long succession of detectives in white suits trooped in and out of 39 Killakee Walk, where Mary Keegan and her sons, Glen (10) and Andrew (6), lay dead in the kitchen. Gardaí were discreet about what they witnessed inside, one man saying only that it was "quite a scene".
The first forensic investigators entered the house through the back garden, using ladders to climb the wall. As evidence from the hallway was gathered, later arrivals, including Deputy State Pathologist Dr Michael Curtis, were able to go in via the front door. A local priest, Fr Patrick Madden, visited the scene briefly to pray outside.
Residents of Killakee Walk stood in their driveways, recalling the normal, happy family on which such horror had been visited. Teenager Sinead Mooney remembered speaking to Mary Keegan last Friday, and described her as someone who was "very protective" and "cared so much" about her children. Peter Hale, who lives at number 33, spoke of "a lovely family, with no domestic problems".
Nobody seemed to have seen Mary or her sons over the weekend, however. In one house, where Andrew was a daily visitor, his failure to call for three days was said to be "unusual".
By early afternoon, children from the schools where Glen and Andrew were pupils began arriving at Killakee Walk, with wide variations in their understanding of what had taken place.
The female garda supervising the cordon was a magnet for their inquiries. Evan Tobin (7), who described himself as "Andrew's best friend", asked her if the two boys would be able to watch DVDs in "heaven". A harder-headed older boy wanted to know: "So is some mad fella going around breaking into people's houses?"
The gardaí fielded their multiple inquiries with gentle good humour, in between recording the identities of investigators seeking to pass the tape.
Luke McAvinue (9) arrived in his Scoil Treasa uniform, knowing - via his teacher - "something very sad" had happened. A classmate of Glen's, he had played hurling with him on the school team, and they normally trained on Mondays. He asked reporters and the female garda what they knew, and they told him softly. "It's very sad," he said again.
The crime-scene cordon was a wide one, embracing not only the end of Killakee Walk, but part of the car park in the adjacent shopping centre and even one side of Firhouse Road, on to which the housing estate opens. But, as the evening passed and the bodies were removed by ambulance, it was clear the investigation was narrowing and this had been a very domestic tragedy.