|Criminal trials and convictions|
|Rights of the accused|
|Related areas of law|
In Canada and England and Wales, certain convicted persons may be designated as dangerous offenders and subject to a longer, or indefinite, term of preventive detention in order to protect the public.
In Canadian criminal law, a convicted person who is designated a dangerous offender may be subjected to an indeterminate prison sentence, whether or not the crime carries a life sentence, but this does not apply to convictions of first degree murder, second degree murder, high treason, and treason. The purpose of the legislation is to detain offenders who are deemed too dangerous to be released into society because of their violent tendencies, but whose sentences would not necessarily keep them incarcerated under other legislation, such as the Correctional and Conditional Release Act. Under subsection 761(1) of the Criminal Code, the Parole Board of Canada is required to review the case of an offender with a dangerous offender label after seven years, and parole may be granted as circumstances warrant, but the offender would remain under supervision indefinitely. After the initial review, the Parole Board must conduct subsequent reviews every two years. According to Corrections Canada, on average 24 dangerous offenders are admitted to the Canadian prison system each year. Paul Bernardo is one well-known dangerous offender.
The dangerous offender provisions have been found constitutional: "The individual, on a finding of guilty, is being sentenced for the 'serious personal injury offence' for which he was convicted, albeit in a different way than would ordinarily be done. He is not being punished for what he might do. The punishment flows from the actual commission of a specific offence."
On October 17, 2006, the Canadian government introduced legislation that made it easier for Crown prosecutors to obtain dangerous offender designations. The amendments provide, among other things, that an offender found guilty of a third conviction of a designated violent or sexual offence must prove that he or she does not qualify as a dangerous offender. This legislation was passed in 2008. Under previous legislation, the Crown had to prove that the individual qualified as a dangerous offender. The amendment reverses the onus for individuals convicted of three violent offences. Such individuals must now demonstrate to a court that despite the three convictions, they should not be designated as dangerous offenders.
Canadian courts also have the option of designating convicts "long term offenders". A hearing is held after sentencing, and, if a judge rules the accused is likely to re-offend after release, a 10-year period of community supervision is required after the sentence is completed.
United States 
The "dangerous offender" approach is constitutional in the United States where a person convicted of a crime may be held past the statutory maximum for a crime if the courts deem such person to be a "dangerous offender", as defined by the statute in the state of prosecution. "Dangerous Offender" statutes are defined on a state by state basis, and are applied at sentencing such that the enhanced "Dangerous Offender" sentence stems from the original illegal activity. Person under "Dangerous Offender" sentences are typically held for a minimum term that coincides with the sentence the person would have received without the "Dangerous Offender" sentence, and thereafter is subject to review of the person's state of mind as a determination of eligibility for release. If there is a question that the person may continue to be dangerous, he can be civilly committed if, through a judicial hearing, it is determined that a concurrent mental disorder makes it likely that he will continue to be dangerous because he lacks any self control. This issue arose in the case of sex offenders in Kansas v. Hendricks (1997) in which the court did allow limited commitment, but it reversed itself on the very same issue in Kansas v. Crane (2002), imposing much stricter commitment standards. Since such a high burden of proof can be met only rarely, there are a variety of state and federal sex offender registration laws geared to protect the public. The constitutionality of these have been upheld by the United States Supreme Court in Smith v. Doe (2003).
England and Wales 
In Denmark, repeat offenders who commit dangerous crimes, such as murder, arson, assault, rape, child molestation or robbery may be sentenced to indefinite detention. This sentence is usually bestowed on repeat sex offenders; it is not usually used on offenders who otherwise would merit a life sentence. The detainees are housed in Herstedvester Prison Detention Centre (The Institution of Herstedvester), west of Copenhagen, and they serve in average nine years before being paroled with a five-year probationary period.
- Criminal Code definition of 'serious personal injury offence, which is the basis for a dangerous offender application
- Criminal Code, R.S.C. 1985, c. C-46, s. 752
- R. v. Lyons
- "Minister of Justice Proposes Stringent New Rules to Protect Canadians from Dangerous and High-Risk Offenders". 2006-10-17. Retrieved 2007-03-07.
- "Children's Bureau Express Online Digest: Supreme Court Decision Will Impact Civil Confinement of Sex Offenders". cbexpress.acf.hhs.gov. Retrieved 2008-03-15.[dead link]
- "Smith et al. v. Doe et al.". caselaw.lp.findlaw.co. Retrieved 2008-03-15.