Year and a day rule

The application of the rule was a custom of English law that became enshrined in common law. The rule was abolished by a Law Reform Act in 1996. English law is now substantially revised such that if an act can be proved to be cause of death, it can now constitute murder regardless of the intervening time. The abolition of the rule does not relieve the prosecution of its obligation to prove, in cases of murder, that the accused intended to cause either death or serious injury.

Principally, the rule was abolished due to the advancement of medicine. Life support technology can extend the interval between the murderous act and the subsequent death. Application of the year and a day rule prevented murder prosecutions, not because of the merits of the case, but because of the successful intervention of doctors in prolonging life. Additionally, advances in forensic medicine may assist the court to determine that an act was a cause of death even though it was carried out fairly far in the past.

In England and Wales, the permission of the British Attorney General is required for any prosecution in which it is alleged that the death occurred more than three years after the causative act, or when the offender has previously been convicted of an offence in connection with the death.

The rule's status in the United States is less clear: many states have abolished it completely, and in 2001 the Supreme Court held that a Tennessee court's retroactive abolition of the rule was constitutional (Rogers v. Tennessee). However, its common law status has been successfully used by defendants to overturn convictions as recently as 2003.[1] (http://www.greenbaypressgazette.com/news/archive/local_10331375.shtml)

Other legal and quasi-legal uses of year and a day
The period of a year and a day was a convenient period to represent a significant amount of time. Its use was generally as a jubilee or a permenance.
Historically (England) the period that a couple must be married for a spouse to have claim to a share of inheritable property.
In mediaeval England, a runaway serf became free after a year and a day. Hence the saying "Town air makes free."
When a judgement has been reversed a fresh action may lodged within a year and a day, regardless of the statute of limitations. USA
In USA a common sentence length e.g. computer cracker Adil Yahya Zakaria Shakour was sentenced to one year and one day. Ref: USDOJ (http://www.usdoj.gov/criminal/cybercrime/shakourSent.htm) For some crimes this is the minimum penalty.