‘Multiple personality’ research calls for better guidance for police interviews

Police officers and intermediaries face significant challenges and may need better guidance when it comes to interviewing some vulnerable witnesses, new research suggests.

The University of Portsmouth study is the first to examine the challenges of interviewing people with dissociative identity disorder (DID), a complex disorder characterised by two or more distinct personality states. DID is also known as multiple personality disorder.

The researchers focused on the role of intermediaries – specialists in communication who advise on the interviewing of vulnerable witnesses – and found limited experience of the complex condition, a lack of research in the area and no legal guidance for police officers and intermediaries.

Lead researcher Dr Brendan O’Mahony, a visiting research fellow at the University’s Centre of Forensic Interviewing and a registered intermediary, said: “There has been a substantial amount of psychological research about the appropriate questioning of children and people with an intellectual disability and the findings have led to best practice guidelines for police interviewing and for the questioning of witnesses at court.”

“However, there has been limited research on how mental disorder and mental distress impacts on effective investigative interviewing. The dearth of DID cases apparently going to trial at court, as identified in part by this research, might suggest that people with a DID diagnosis may be marginalised from the justice system. There is certainly a lack of guidelines for professionals on effective questioning of these vulnerable complainants, both at the police station and at court.”

A forensic psychologist, Dr O’Mahony was inspired to carry out the small exploratory study after being asked to act as an intermediary for witnesses with DID and seeking extra training. He realised there had been no published research examining the potential communication difficulties in cases involving witnesses with DID and other conditions where people experience dissociation (disconnecting from the present environment to cope with stress).

People with DID may present alternative personalities during interview as well as their ‘normal’ or ‘host’ identity and sometimes have no understanding of the experiences, feelings and thoughts of their different identity states.

Dr O’Mahony said: “Establishing a rapport with a witness can be very difficult in these cases and then you still don’t know the extent of the dissociation. One of the issues facing police interviewers and intermediaries is that they may not know which ‘personality state’ is being questioned as the ‘switches’ from one identity to another aren’t always obvious.”

He added: “The complainant may also be experiencing an internal dialogue which the interviewer is unaware of, with one of the emotional personalities (alter) telling the host not to ‘trust’ the interviewer, for example. The interviewer may be unaware why the conversation ceases.”

The study, published in the Journal of Forensic Practice, notes that many intermediaries – who range from psychologists to occupational therapists, social workers, mental health workers and speech and language therapists – are expected to provide communication advice to the police and courts about how to manage communication with the host and alters in circumstances where there is no formal guidance.

Dr O’Mahony collaborated with Professor Becky Milne at the University’s Centre of Forensic Interviewing and Dr Kevin Smith, who is the National Vulnerable Witness Adviser at the National Crime Agency, to work on the small study which identified 20 cases of intermediaries advising on apparent DID cases. A questionnaire was subsequently completed by four intermediaries. Dr O’Mahony called the intermediaries who engage in this work ‘groundbreaking’ and hoped his research would inspire further investigation.

The researchers recommended that the police and intermediary team should only match DID cases with intermediaries specialising in DID. They also called for guidance from the legal profession as to what type of evidence would be admissible in court.

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