For more than two hours, the killers moved undetected among the houses of Itamar.
They had climbed the electronic fence surrounding the settlements at 9pm, triggering a message to the local security centre.
A civilian guard was sent to check but saw nothing in the darkness, dismissing it as possibly an animal. He did not notify the nearby IDF outpost.
In minutes, the two men had crossed the woods between the fence and the first line of houses at the southernmost edge and broken into one of them. The owners were away for Shabbat. They stole a rifle and left.
Seeing through the windows that the family next door were still awake, they waited for over an hour before breaking in. Armed with knives, they first entered the bedroom where 11-year-old Yoav and four year-old Elad Fogel were sleeping. They stabbed them both. Their mother, Ruth, 36, heard screams and rushed to their room with a rifle, firing a single shot before being overpowered.
They then went to the parents' bedroom where they murdered the father, Udi, 35, and his three-month-old girl, Hadas. Throughout, two other children, Ro'i, eight, and two-year-old Yishai remained asleep. By 11pm the men were back at the fence. Their passing was once again registered and dismissed.
The bodies lay undetected for a further 90 minutes until the family's eldest daughter, Tamar, 12, returned home from Bnei Akiva to make her harrowing discovery.
It took a further two hours before the army could be certain that the murderers had left the settlement. They searched dozens of homes in the nearby Palestinian village of Awarta, a short walk from the fence. The village remained under curfew until Wednesday. Hundreds of men were questioned and some were taken for interrogation by the Shin Bet. At the time of going to press, no official announcement had been made regarding the findings.
The IDF is now reviewing security procedures and examining the conduct of both civilian and military personnel. The findings will be presented to the IDF high command - which is expected to draw serious conclusions regarding local officers.
"It was a horrendous and barbaric attack that is hard to connect to any known kind of human behaviour," said IDF chief of staff, Lieutenant General Benny Ganz. "I am certain that we will put our hands on the murderers before long."
Driving into Itamar, deep in the West Bank this week, you could be forgiven for thinking that nothing of any consequence had happened only days earlier. The settlement checkpoint is unmanned and, further along, a child could be seen casually trying to hitch a lift from passing cars. Here and there labourers put up new homes, and a man carefully paints a kerb.
Even at the house where the murders took place, only police tickertape gives any hint of the horror.
A child's bicycle stands next to the porch, washing lies on the ground and on the front door is a note announcing the birth of baby Hadas.
Five doors away, neighbour Yaakov is playing in his front garden with his three small children.
On the night of the attacks, he was awoken by the sound of a shot. "It was my neighbour," he said, "who was alerting the security team."
It was to that neighbour's house that Tamar Fogel ran after discovered five members of her family lying dead.
Surely, he is afraid now - especially about the effect on his children? "We don't talk about it much. The important thing is to carry on living," he says, lifting a toddler out of a flowerbed. "But the children know the details. The ones who can speak can explain what happened better than the grown-ups.
"There was an attack like this eight years ago. Back then there were only 60 families here. Since then we've doubled our numbers.
"Where that family lived, there is now another family. We will do the same here."
Yaakov points to the slope behind his house, the direction from which the attackers came. Visible just beyond the trees, on the opposite hilltop, is the Awarta, the village closed off by the Shin Bet. "We will build another line of houses down there," he says. "This is our response."
Moshe Goldsmith, the de facto mayor of Itamar, says: "This was a family of angels. You have to be a robot not to feel broken by this. We have suffered more tragedy than almost any other community.
"We have to work as hard as we can to heal the wounds, and make life continue as normal."