Warning: this article contains explicit and disturbing content.

German police earlier this week were reported to have arrested Luka Rocco Magnotta, a former porn actor suspected of mailing severed body parts to Canadian political party offices, but in the meantime yet another series of grisly twists have emerged in this harrowing tale.

Two of the victim's missing body parts - a right hand and a right foot - have now been recovered after they were posted to schools in Vancouver from Montreal, the city in which it is suspected a missing 33-year-old Mr Jun Lin, was allegedly murdered by Magnotta.

On Tuesday last week Canadian police found a human torso in a suitcase behind Magnotta's Montreal apartment. He is suspected of killing Mr Jun Lin and filming the act. Posted online, the video is apparently graphic and disturbing, portraying a man stabbing a naked and bound victim with an ice pick. The man apparently later boasts he has slashed the victim's throat, then he dismembers the corpse and seems to perform sexual acts with it. A severed foot was also found in a package mailed to the Conservative Party headquarters in Ottawa while a hand was discovered in a separate package addressed to the Liberal Party of Canada.

Forensic Psychologist Helinä Häkkänen-Nyholm, a former criminal profiler with the Finnish police and Adjunct professor at the University of Eastern Finland and University of Helsinki, comments that what seems to be unique in the Magnotta case is the fact that the body parts are sent to others. She sees this as a reflection of attention and sensation seeking, grandiosity and narcissism. It is likely, she contends, that he has fantasised many times the reactions that opening the mail will provoke.

She has also found from her experience that lack of empathy and inability to properly experience emotions are characteristic of this kind of killer. Dr Häkkänen-Nyholm argues that you cannot presume that the offender would have felt anxiety, horror or guilt when performing these acts. She was once involved in an interview with an offender who had eaten some of his victim's body parts. He told his interrogators that he ate them precisely because he was aiming to feel something. When he was asked "so how did it feel?" he said that he didn't know, because it felt no different to anything else in his life.

Dr Häkkänen-Nyholm, the author of numerous scientific publications on violent behaviour, contends that the allegations over the filming of various aspects of the recent crimes could serve the same purpose as sending the body parts to someone does: it supports the grandiose thoughts the killer has of himself. She says similar behaviour occurs in school shooting cases where the shooter has made a video of himself playing with the gun and rehearsing. This happened in both of the recent school shooting cases in Finland.

Dr Häkkänen-Nyholm suggests that usually in this type of case, the fantasies serve the purpose of feeling superior to others, hence fantasised images of creating horror and gaining attention through the criminal behaviour are likely. In reality the offender's self-image is often disturbed and negative, although they may appear to some as self-confident.

Helinä Häkkänen-Nyholm, Eila Repo-Tiihonen and other Finnish academic colleagues have published one of the definitive pieces of research on this kind of gruesome killing in a paper entitled 'Homicides with Mutilation of the Victim's Body' and published in the prestigious 'Journal of Forensic Sciences'.

Being an extremely rare crime - around 2% of homicides in their part of Europe involve mutilation or dismemberment, while in other parts it's down to one in 500 murders, it's very difficult to perform definitive research, but the authors of this review did report some worrying evidence that this particular kind of murder could be increasing in some parts of the world, such as Germany and Japan.

Researchers suggest there are five main different kinds of homicidal mutilation; possibly the most common is referred to by Forensic Specialists as 'defensive' because the motive is to assist in hiding or moving the body, or getting rid of evidence, or making identification of the victim more difficult.

In a case reported by Tomasz Konopka, Jerzy Kunz and colleagues from the Department of Forensic Medicine, Collegium Medicum Jagiellonian University, Krakow, Poland, human skin dissected free from a torso and other body parts were recovered from a local river. The remains were established to be those of a female student, who had been pronounced missing two months previously, but perhaps because of the delay in identification, the perpetrator is described in the paper as unknown.

The second most likely motive or category for this sort of mutilation murder is frequently found to be 'aggressive' - where the killing and mutilation is brought about by the same aggressive strong emotions, they are part of the same emotional motivation. A sub set of this type might be where dismemberment is in fact the cause of death, for example dismemberment as means of torture.

In their series of cases collected in order to spot patterns 'Corpse dismemberment in the material collected by the Department of Forensic Medicine, Cracow, Poland' and published in the journal Legal Medicine, Tomasz Konopka, Jerzy Kunz and colleagues draw attention to a case when several perpetrators, both male and female, from the Middle East, executed an alleged traitor, severing parts of his face, genitals and inflicting more than 100 incised and stab wounds while the victim was still alive.

The third most common category is usually referred to as an 'offensive' mutilation where the dismemberment is in fact the real purpose of the murder all along, and these include lust and necro-sadistic murders. Those driven by primarily sexual motives mutilate the corpse in characteristic ways, Konopka, Kunz and colleagues report, for example severing genital organs or breasts. Some perpetrators pull out abdominal organs through the disfigured genital tract. Death by strangling is apparently very common in this kind of homicide.

In the fourth category are 'psychotic' murders where the perpetrator has lost touch with reasoning and perceptual reality in the conventional sense, so that they may be hearing voices or they suffer from bizarre delusions. Kamil Hakan Dogan, Zerrin Erkol and colleagues report just such a case in their paper entitled, 'Decapitation and Dismemberment of the Corpse: A Matricide Case' published in the Journal of Forensic Sciences. A 57-year-old woman was decapitated and her right arm and both hands were dismembered by her 33-year-old daughter, who had been receiving treatment for schizophrenia for 15 years.

This case in no way suggests that schizophrenia in itself is a particularly dangerous psychiatric condition.

In the fifth type of dismemberment, are the kinds of killings associated in the modern world with organised crime such as the Mafia, whereby mutilation or dismemberment is a way of sending a message to others - in this case the murder isn't just about getting rid of someone - it's also a form of communication - a warning or threat.

In a clue as the kind of person the Canadian police might be looking for, the Finnish academics found mutilation and dismemberment murders was significantly associated with childhood sexual victimization, particularly compared to other kinds of murderer. Surprisingly, given some specialists in the area had suggested that abattoir workers, mortuary attendants or butchers may be more represented in this group of killers, as occupational access to corpses or anatomical knowledge might be required, yet in the Finnish study, none of the perpetrators had an occupation which required anatomical knowledge or handling corpses.

What Helinä Häkkänen-Nyholm, Eila Repo-Tiihonen and colleagues did find is that these killers were almost twice as likely to have been violent at school as other kinds of murderer, and there was a much higher likelihood of past contact with mental health services compared to other homicide offenders. Only one perpetrator of mutilation homicide had never been in contact with psychiatry yet ten out of 14 offenders in the Finnish study had been in-patients.

The authors of this study report the key clue from their research which they believe will assist in tracking down these killers in the future is that unlike other kinds of homicide, the offender is always known to the victim, in nearly half of the cases being a family member or a partner.

Most psychiatric illness is not associated with violence, indeed many psychiatric patients are often more vulnerable to being attacked, than the other way round. What this recent research might suggest is that much better access to higher quality educational, social and psychiatric services from an early age, for the whole community, could possibly contribute to improving prevention of this rare crime.

Dr Raj Persaud, Consultant Psychiatrist based in London, and Dr Helinä Häkkänen-Nyholm, former criminal profiler and academic based in Finland. She currently runs the psychology and law firm PsyJuridica Ltd.