5) Sexual slumming?
Kirwan was unmarried, and we know from his pawnshop activities that he sometimes liked to play at being poor. He wouldn't be the only Victorian gent to use underclass women as a source of sexual relief.
I can believe he might have stopped off in Southwark to find a whore - perhaps even one like Roberts - but that does not explain why be chose to linger there all night. Why not spend his ample funds on a rather more appealing woman or, if Roberts' lowly status was part of the appeal, why not go back to his nice warm bed when the deed was done? "Doctors can lead double lives, and he wouldn't have been the first to visit a prostitute," our own doctor admitted. "But, as you say yourself, he'd want to go back to a comfortable bed." (27)
If this was part of a wider masquerade Kirwan indulged in for some reason, perhaps using his George Allen alias, then why not go the whole hog and dress in rags too? He must surely have known that wandering round Southwark in a top hat and all his other finery would mark him out as a toff and therefore put his life in severe danger. (28)
6) A stroke or seizure?
Having rejected all the above theories one by one, I was left with the idea that Kirwan may have suffered something like a minor stroke after he left the Aberfeldy on Tuesday night.
I imagined him innocently on his way home when this neurological disaster strikes, leaving him so confused that he abandons his journey in Southwark and begins walking aimlessly round the streets there. Sooner or later, Roberts finds him stumbling along, mistakes him for a drunk, and decides he's source of easy cash.
Perhaps she offers him sex, or perhaps she merely takes him by the arm and persuades him to buy her a drink. By this time, he's helpless enough for Roberts to lead around at will. His brain, the very instrument which would once have allowed him to diagnose his condition, is now so damaged that he barely knows who he is.
Waller and the rest start trailing him too, and the rest we know. Apart from occasional brief rallies - fighting off the Redcross Way mugging attempt, casting away his second beer in The Lord Clyde - Kirwan gets steadily worse as the day wears on until he's dragged up Whitecross Street barely able to walk.
Once again, though, Carling's autopsy report seems to rule this out. "He might have have a small stroke or a small cerebral bleed," our doctor said. "But you have to believe that would have been picked up on the post mortem, because they looked at his brain quite carefully. If he'd had a head injury or if he'd had a bleed? They'd have picked up those major things.
"If it was a stroke, you might expect him to have a weakness down one side, or slurred speech, and there was nothing. He was certainly moving all four limbs by the sound of it. So there's nothing to suggest he'd had a major stroke. Bleeds can progress and build up, but normally you get a blinding headache and it knocks you to the ground. The reports are that he was absolutely fine and behaving totally normally the night before, and there was nothing to suggest that he was ill."
Our coroner came to the same conclusion when considering the possibility of a seizure. "Unusual behaviour may follow fits (a post-ictal state) or psychiatric problems (a fugue state)," he told me. "But there is no previous history here."
7) Acute intermittent porphyria?
This is the disease now thought to explain the supposed insanity of King George III, as depicted in the Alan Bennett play and the film that followed it. In George III's case, the condition's believed to have been triggered by attempts to poison him with arsenic, but our doctor told me that booze could do this job equally well.
"Acute porphyria can be triggered by alcohol," he explained. "It would give rise to acute confusional states, often triggered by alcohol or drugs, and to acute abdominal pain. Now, if you look at the report carefully, Kirwan clearly had acute abdominal pain. He was curled up. Lizzie Williams said he was very pale in the face - and that's a classic feature of acute abdominal pain. And he was slumped over: they had to support him. That would fit very nicely."
Porphyria would never have occurred to me without this steer, but when I did a bit of research I discovered that its acute form does fit much of Kirwan's behaviour. "Signs and symptoms appear quickly and usually last a short time," the Genetics Home Reference site says. "Episodes of acute porphyria can cause abdominal pain, vomiting, constipation and diarrhoea. During an episode, a person may also experience muscle weakness, seizure, fever and mental changes such as anxiety and hallucinations". (29)
A couple of paragraphs later, the same site names alcohol as one of the factors known to trigger attacks, adding that AIP is the acute disease's most common form and that it's thought to be found most often in northern European countries such as the UK. (30)
Kirwan certainly didn't show all these symptoms, but he did exhibit a fair sprinking of them. A sudden attack followed by a bout of confusion would explain both his aborted attempt to get home, and his night wandering the streets of Southwark. We have descriptions of him doubled over with pain in The Lord Clyde and looking very pale a few minutes later, both of which suggest severe abdominal pain. (31)
The pharmacist watching Kirwan in The Lord Clyde thought he had delerium tremens, which shows many of the same symptoms as porphyria, including confusion, anxiety, hallucinations and extreme sensitivity to light. The muscle weakness seems to fit with Kirwan's weariness in the flower shop and the fact that his legs would barely support him later. James Rothwell saw him staring around wildly and looking worried in Redcross Gardens, which suggests anxiety and, perhaps, that he was suffering hallucinations too.
Porphyria was not identified until 1889, and would have still been very little understood when Kirwan died. Even as a medical man, he'd have had scant chance of identifying his condition, and I doubt Carling knew enough to consider it in the autopsy either. To the uneducated folk of Southwark, most of Kirwan's porphyria symptoms - if that's what they were - could easily have been mistaken for simple drunkeness. Finding himself confused on the streets of Southwark, he gets picked up by Roberts, and the rest plays out as in the stroke scenario above.
"Porphyria would fit nicely with his presentation of acute confusion," our doctor told me. "Being in the wrong place at the wrong time, and wandering. Porphyria can do this. It can come on very acutely - one minute you haven't got it, and the next minute you have."
I put this idea to Liz Gill of the British Porphyria Association, but she was sceptical. "As an acute prophyria sufferer, it seems to me quite unlikely that this would be the answer," she said. "Personally, I think you were probably more on the right track with a stroke."
If Kirwan really was a porphyria sufferer, Gill told me, and if alcohol was his trigger, then he'd most likely have shown symptoms of pain after drinking on previous occasions - and yet neither his friends nor his landlady mention anything like this. As far as a full-blown attack is concerned, Gill thinks it would have taken quite a lot of alcohol to push Kirwan over the edge.
"Alcohol is generally thought to be a problem [only] in fairly large quantities," she said. "Although we still advise acute prophyria patients to avoid alcohol, many sufferers do have small amounts to no ill effect." Kirwan policed his drinking very carefully most of the time - perhaps because he knew it caused problems otherwise - but there's no evidence of an uncharacteristic binge when he reached Southwark.
And that, I fear, is about as close as we're likely to get in discovering why Kirwan behaved as he did. We have one vote in favour of poisoning, one in favour of porphyria and one in favour of a stroke - but also some powerful points against all those theories. Unless someone out there has a blinding flash of insight or some new information to offer, The Borough Mystery looks set to remain just that.
To see what the playwright Arthur Wing Pinero made of William Kirwan's murder, please visit PlanetSlade's May 2013 letters page here.
For Sources & Footnotes, please see next page.