Sir Michael Fallon's written a letter apologising to the mum of a Tamworth soldier - who was killed by a roadside bomb.
PM Says 'No Punishment In The World' Fit For Staffordshire Mum Who Killed Toddler
The Prime Minister says there's no punishment in the world that fits the crime of a Staffordshire mother who stamped on and killed her daughter.
The Prime Minister also pledged to examine concerns over the independence of an investigation into the "despicable and disgusting'' death of 21-month-old Ayeeshia Jane Smith.
But he said the serious case review must get under way as there is a need to "get to the bottom of what went wrong''.
Kathryn Smith, 23, was jailed for at least 24 years after being convicted of murder at the family home in Burton-upon-Trent, Staffordshire, on May 1 2014.
Ayeeshia's stepfather, 22-year-old Matthew Rigby, was jailed for three years and six months after he was convicted of causing or allowing the death of a child.
Mr Cameron said the description of the child's death "simply took your breath away''.
Conservative Andrew Griffiths raised Ayeeshia's "tragic death'' during Prime Minister's Questions, telling MPs the toddler's heart was punctured, while a pathologist said her body "resembled a car crash victim''.
Burton MP Mr Griffiths added to Mr Cameron: "Yet Ayeeshia had been known to social services since the day she was born.
``They knew about the violent boyfriends, they knew about the domestic violence, they saw the doors kicked in, they smelt the cannabis, they saw the bruises, they saw the cuts, they saw the fingerprints on her little thighs - and they did nothing.
``You will understand that people in Burton want to know how this could have happened, yet they are concerned to know that the serious case review has on its panel people who are directly involved in the organisations being investigated.
"Will you look at what we can do to make this and other serious case reviews more independent so that we can make sure that no other child suffers the life and the death of Ayeeshia Jane Smith?''
Mr Cameron replied: "In the work that we all do we get to hear about some hideous and horrific incidents but anyone watching television that night and seeing the description of what happened to Ayeeshia, it simply took your breath away that people could behave in such a despicable and disgusting way towards their own children.
"There's no punishment in the world, in my view, that fits that sort of crime carried out by the child's own parent.
"As you say, there will be a serious case review. I'll look very carefully at the suggestions that you make, I know (Education Secretary Nicky Morgan) will do so as well.
"There are criticisms of the way these cases are done but I think to start with in this case we must get on with the serious case review because we've got to get to the bottom of what went wrong.''
A Black Country man's been jailed for life for stabbing his partner. Ronald Cooke attacked Tina Billingham at their home.
The family of 20 year-old Callum Lees, who was stabbed to death at a house party in Solihull, have paid tribute as they appeal for his killer to come forward.
The binmen strike in Birmingham by members of Unite the union has been suspended.
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