Det Supt Mick Mason said the traumatic nature of the incident had affected many of the officers who worked on the case, but it had seemingly provoked little reaction from the brothers themselves.
"You think of the severity of the attack, it must have sunk in and they must be realising what they have done. I'm not sure about that.
"From what I'm told, they didn't show any remorse during interview."
Children's Secretary Ed Balls, who said his response was the same as many families across Britain, described it as a "horrific" case.
He said: "These are children who, to be honest, have been deeply damaged by years of abuse - physical abuse, seeing their mother being struck by their father, but also abuse against them.
"But that's no excuse for what they did.
"What we've now got to do is make sure that in custody they get the support to try and turn things round for them.
"And we also learn lessons in Doncaster so that in future we don't have a repeat of such a terrible, unusual and horrific case."
Andrew Flanagan, chief executive of the NSPCC, said England had "not seen such acts of schoolboy savagery for many years".
He said: "The case raises serious questions about how children can be left to drift in homes seriously damaged by violence and neglect.
"Where families cannot give their children a decent start in life, the authorities need to act swiftly and robustly - both for their sake and the rest of society."
A BBC investigation has revealed the two attackers were well-known troublemakers and social services were heavily involved in their lives.
A Safeguarding Children Board report, seen by BBC Newsnight, found the attack could have been prevented.
Sue Berelowitz, the deputy children's commissioner for England, said: "The best way to end these cycles of violence is to ensure that the relevant services respond quickly and effectively when children are seen to be at risk.
"If reports of the serious case review in the newspapers are accurate, there is no doubt that support services missed many chances to identify these brothers as being capable of committing appalling crimes, and this is of deep concern."
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