Serial Killer Fiction

I'm writing a novel set in modern England about a serial killer and I'm intending to make the book as accurate as possible. I'm trying to avoid creating something along the lines of Hannibal Lecter or Patrick Bateman. I've already pieced together a character profile that fits the model of an organised hedonistic serial killer according to the FBI behavioural science unit.
The whole story takes place in an interrogation room, where forensic psychologist Dr Rymdzionek interviews suspect Phillip Hammel. Basically he confesses in gory detail and the story of his killing spree and subsequent downfall is told in non-linear flashbacks.

Phillip Hammel-38 years old at the time of the story, but he began killing at the age of 24. He is convicted of 7 murders but there could be a lot more. He's an organised offender which means his murders are meticulously well planned and prepared. He gets a sense of power through killing. Hammel's MO consists of torture, decapitation and necrophilia. Hammel has nocturnal habits and keeps hiding places in his house, he also has an obsessive interest in the media and the police. He has an active social life but his sex life is inactive or maybe he's married with kids, I haven't decided yet. He attended college and possibly university, I haven't decided on what occupation he should have.

Dr William "Liam" Rymdzionek-Liam Rymdzionek is 45 years old brilliant psychologist working as a consultant for murders being investigated by the CID. He's a married man with two children. He is a workoholic who neglects himself and his family during cases. He is also a recovering drug abuser and alcoholic, though he remains a recurring abuser of alcohol.

What I need is a fantasy for my killer something along the lines of mother or sister issues maybe. I've looked all over the net for information on serial killer fantasies and in-depth analysis of killers by forensic psychologists, but I can't find anything that has great detail. Any suggestions on changes I could make are very much welcome.

Thank you in advance for all suggestions and advice.