A man whose sister and nephew were shot dead by his brother-in-law in 2003 is set to challenge a ground-breaking review of the case at the High Court.
After the shootings, Alan Pemberton (right) turned the gun on himself
Frank Mullane, from Swindon, Wiltshire, believes a major probe into the murders of Julia Pemberton and her son, William, will not be broad enough.
They were killed by Alan Pemberton at their home in Hermitage, Berkshire.
Mr Mullane believes police failed to take steps to prevent the murders despite clear warning signs.
At the time of the shooting, Pemberton - who turned the gun on himself - was separated from his wife and was the subject of a court order banning him from going anywhere near the property because of threats.
Last year, a "homicide review" into the case was set up after Mr Mullane met Home Office Minister Baroness Scotland.
The review is set to be the first of its type in the country and is expected to shape how investigations into similar tragedies will be carried out in the future.
But Mr Mullane is applying for a judicial review of the terms of reference of the probe.
He is set to argue that it falls short of Article Two of the European Convention on Human Rights - the right to have life protected by law.
Issues aired at a hearing in London on Wednesday are expected to include the involvement of Mrs Pemberton's family and the use of independent experts, Mr Mullane said in a statement on Monday.