Another statement of the concept of due process guaranteed by the US Constitution's Fifth and Fourteenth Amendments.
Human Rights Act 1998 incorporates into English law Article 2
Convention for the Protection of Human Rights and Fundamental Freedoms,
which defines the right to life as follows:
right to life shall be protected by law. No one shall be deprived of his
life intentionally save in the execution of a sentence of a court
following his conviction of a crime for which this penalty is provided
2. Deprivation of life shall not be regarded as inflicted
in contravention of this Article when it results from the use of force
which is no more than absolutely necessary:
(a) in defence of any person from unlawful violence;
(b) in order to effect a lawful arrest or to prevent the escape of a person lawfully detained;
(c) in action lawfully taken for the purpose of quelling a riot or insurrection."
The reason that "get away with murder" laws violate due process is that they sanction the extra-judicial taking of life, which contradicts 800 years of legal history.
BTW, In Evans v United Kingdom, the Court ruled that the right to life does not extend to a human embryo.