Labour peer Lord Greville Janner of Braunstone will not face charges over child abuse allegations because he has dementia, the Crown Prosecution Service said on 16 April 2015.
Alison Saunders, the director of public prosecutions, said it is not in the public interest to charge the former MP as the "severity of his condition" means he is unable to stand trial. Had he been mentally fit, Janner would have been charged with a total of 22 child sex offences occurring between 1969 and 1988.
Leicester Police, who are investigating allegations of child abuse at Leicestershire care homes between the 1960s and 1980s, described the decision as "the wrong one" as there is evidence Jenner committed the "most serious sexual crimes imaginable".
Janner was previously investigated for child sex offences in the early 1990s, but police were told not to arrest or search the home of the MP. The CPS added it now considers that "some of the decisions made by both itself and by the police in relation to past investigations relating to Lord Janner were wrong".
Saunders said: "The CPS has carefully considered whether it is appropriate to make a public statement in relation to this case, explaining the reasons for this decision and has decided that it is appropriate to do so.
"There has been considerable public interest, and media coverage, of the fact of the investigations including identifying Lord Janner as the subject of them.
"Indeed, concern has been expressed publicly of a 'cover up'. The allegations that have been made against Lord Janner are extremely serious. Those who have made them are, entirely understandably, vociferous in urging the taking of action against Lord Janner.
"The reasons for the decision not to do so require explanation in some detail in order to be properly understood and to avoid the inevitable speculation that would follow were no explanation to be given. It is a matter of deep regret that the decisions in relation to the previous investigations were as they were.
"Had the previous decisions been to prosecute, as they should have been, Lord Janner would have had the opportunity to challenge the evidence and defend himself through the trial process, with a jury ultimately deciding on his guilt or innocence some years ago.
"Victims of the alleged offences have been denied the opportunity of criminal proceedings in relation to the offences of which they have complained. It is of obvious and particular concern that such proceedings did not take place as a result of what the CPS now consider to be wrong decisions."
In 2009 Janner was diagnosed with Alzheimer's disease, which is the most common cause of dementia, and is said to require "continuous care both day and night".
The CPS added: "[Lord Janner's] evidence could not be relied upon in court and he could not have any meaningful engagement with the court process, and the court would find it impossible to proceed."
Assistant Chief Constable Roger Bannister of Leicestershire Police, said: "There is credible evidence that this man carried out some of the most serious sexual crimes imaginable over three decades against children who were highly vulnerable and the majority of whom were in care.
"I am extremely worried about the impact the decision not to prosecute him will have on those people, and more widely I am worried about the message this decision sends out to others , both past and present, who have suffered and are suffering sexual abuse.
"We are exploring what possible legal avenues there may be to challenge this decision and victims themselves have a right to review under a CPS procedure."