The real life story of multiple murderer Peter Kürten and his tortured lawyer

'Peter, what have you done?' What, indeed, did Peter Kürten do?

Though apparently a mild-mannered middle-aged man, Kürten was convicted of nine murders and seven more attempted murders in the German city of Dusseldorf in 1930. He may have killed as many as 60 people in total though, which earned him the ominous moniker, 'the Dusseldorf Ripper'.

His pickled head found a permanent home in Ripley's Believe It Or Not Museum, but was discarded after scientists dissected it in the hope of answering the question this play ultimately poses: 'Do we bear monsters, or do we create them?'

Author Anthony Neilson is known for his provocative and controversial works. His play about Kürten's life and crimes was written in 1991 for the Edinburgh Festival, and is now brought to the Crescent Arts Centre in Belfast by Green Room productions.

The functional set design consists of two chairs, each on its own platform. By largely confining the actors to their chairs, director Patsy Hughes doesn't add much to the words provided by Neilson. It's minimalist theatre, but it could have been so much more.

Set as Kürten's trial approaches, Normal really is about the killer's lawyer, Justus Wehner (played by Neil McWilliams). The repressed, virginal product of controlling parents, Wehner's time spent with Kürten leads to a crisis of identity. As if naming him 'Justus' didn't sufficiently telegraph his parents' intentions, they mapped out a life at the bar for him, a life of books in which there was no room for love, or indeed life itself.

Wehner's story is one of emotional discovery. Defending Kürten initially seems like a good career opportunity. After all, he only has to prove the man insane, not innocent. But, as he delves into Kürten's past to unearth the roots of his evil, the buttoned-up lawyer gets infected by Kürten's unwholesome appetites.

Eventually we find Wehner brought to his knees, narrating a letter to his parents. 'Why don't you write?' he screams in anguish, before adding a bitter 'Your loving son, Justus'.

There are tears too from Frau Kürten. Gemma Mae Halligan comes across as bland initially, but her performance turns out to be a good interpretation of a woman who, rather than face life on her own, makes tea for her husband's mistress. It's her cry of alarm that runs through the production like a red thread.

Peter Kürten, of course, is also broken, and it's very important for the play to show this damaged human being; outwardly your average, likeable fellow, but with thoughts beneath that veneer of normality that are just not right. This is not what we get though. Instead, Michael Liebmann portrays Kürten as a low rent Hannibal Lecter with slithery voice and twitching cheeks.

While Halligan and McWilliams as Kürten's wife and his lawyer have us on the edge of our seats when fate pushes them closer, the tension snaps when, from the sideline, we hear Kürten hissing: 'Do it, Justussss.'

Modeling Kürten on the Silence of the Lambs icon seems like useful shorthand to portray a serial killer, but that character was only effective when used sparingly. Not confined to the shadows, Kürten quickly fails to unsettle. The end result is more Richard O'Brien than Anthony Hopkins, hamstringing the production.

In exploring the moral questions of good versus evil, Justus Wehner's exposed repression and Eva Kürten's quest for love in disgrace are studies in ambiguous shades of grey. Peter Kürten, however, is painted as just another monster, and is therefore instantly dismissible.