‘Is there any particular reason why he might feel driven to pushing people into the river?’ asked Katie. ‘There are plenty of other ways of killing people at random. You know, like shooting them or running them over. And am I right, or is it not uncommon for a serial killer like this to expect to die himself – either by killing himself or by staging things so that the police kill him?’

‘It depends on his specific delusion. Some want to go out in a massive orgy of self-publicity. They commit one grandiose act of retribution against a world that failed to recognize their needs – like those school shooters in America, who commit a mass murder followed by suicide. Others, though, prefer to draw attention to themselves with a drawn-out series of killings, like our Lee Pusher. They relish the creeping fear that they create in the community, and they love to build on it, gradually, committing one inexplicable murder after another. “You thought you were so superior, did you? Well, I’ll show you!”

‘Sometimes they have a delusion that they have a divine mission to carry out, to teach society a lesson. I don’t know whether you remember but there was a pusher in Limerick about ten years ago. He drowned nine random people in the Shannon before he was caught. He said they were all sinners and he was carrying out the will of God by baptizing them before they died.’

‘I remember him,’ said Katie. ‘He claimed in court that he was the reincarnation of John the Baptist, so he couldn’t be tried by mortal judges, only by angels. Mad as a box of fairies.’

‘Frogs,’ said Kyna.

‘What?’

‘It’s “mad as a box of frogs”.’

‘Well, whatever, he was loopers and you can’t deny that.’

‘So, Dr Power, what do you suggest?’ asked Detective Inspector Mulliken. ‘Is there any specific type of individual you think that we should be looking for? From the few descriptions we’ve been given he sounds like he’s middle-aged, slender build, like, and he always wears a light grey trackie.’

Dr Power said, ‘I guessed at first that he might be unemployed, since he was roaming around in the middle of the day in sports gear. Out of all the murderers and attempted murderers that I’ve given a psychological assessment, about eighty per cent of them are out of a job for one reason or another. That’s usually because they’ve had some pointless argument with their employer or with another member of staff. But then again I think it’s noteworthy that all the pushing incidents took place between one and two in the afternoon, which is when somebody who’s in work would have their lunch break.’

‘The only exception to that was the last one,’ said Katie. ‘That took place early in the evening, about a quarter past six.’