Misguided belief in an 'act of mercy'

The one and two-year-old siblings were found murdered in their Fordingbridge home last month alongside their parents Andrew and Vicky Case. The girls' father is believed to have carried out the killings as he struggled with depression and mounting debts.

Prof Ian Stephen, a city-based expert in criminal psychology who inspired the Cracker television series, said that it was not unusual for parents under the most intense pressure to kill their children in what seems to them to be "an act of mercy".

He said: "The murder element can be an act of mercy in an inverted logic. The thinking is 'I can't go on any longer but I can't leave the children - they will be better off dead because they won't have anyone else to support them'.

"Very gradually, this can be the conclusion they come to. It would be hard for others to spot, apart from people slowly coming more within themselves."

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