Psychopathic criminals are managing to trick correctional staff and parole boards into releasing them back into the community, research claims.

A study published in the journal Legal and Criminological Psychology today suggests criminals diagnosed with psychopathy are more likely to be released then non-psychopaths despite their higher re-offence rate.

The authors of the report explain those criminals diagnosed with psychopathy are characterised by their superficial charm and pathological lying, but lack of genuine guilt and remorse.

For their study the files of 310 male offenders serving at least two years in a Canadian prison between 1995 and 1997, of which 90 were rated as psychopathic according to the Psychopathy Checklist - Revised (PCL-R), were studied.

Offenders classed as psychopathic were around 2.5 times more likely to have been given a conditional release than undiagnosed offenders, the study found.

Meanwhile psychopathic sex offenders were 2.43 times more likely to have been released and psychopathic non-sex offenders 2.79 times more likely.

Dr Stephen Porter from Dalhousie University said: "This is an alarming trend. Psychopathic offenders are far more likely to re-offend, so they should be far less likely to be released.

"However, we found that psychopathic criminals were in fact highly successful in their bids for freedom.

"This could be because psychopaths were better at manipulating their words and actions, and do this to impress and deceive decision makers throughout the correctional system. Using superficial charm and crocodile tears they may be better able to persuade mental health professionals in prison, and eventually parole boards, that they can be successfully managed into the community."

However, another explanation put forward by the authors is that offenders diagnosed with psychopathy appear to make genuine gains in treatment during their prison sentence and positive evaluations in treatment are reflected in the parole board's decision making.

However, Dr Porter argues the appearance of good treatment response in psychopaths is false and they quickly violate their release conditions or re-offend when they return to the community.

"We suggest that professionals who manage offenders in institutions and those charged with releasing offenders back into the community should receive specialised training into the manipulative techniques used by psychopathic offenders to prevent this worrying trend from continuing," Dr Porter adds.

"Although knowledge surrounding the psychopathic personality is more widespread in the correctional system now than when this study was carried out, we still see many examples of psychopaths manipulating the system."