The Medical Evidence

The only facts not disputed by O'Leary were: (1) that Mareo had purchased the veronal that (2) killed Thelma. At issue was whether he had administered the veronal to her and, if he had, whether this had been done either recklessly or with murderous intent. Unlike the infamous Munn trial of 1930, where the accused was charged with and convicted of murdering his wife with strychnine, an obvious obstacle the Prosecution had in Mareo's case was that veronal was a medicinal drug which Thelma might have come to take herself in any number of ways. As the prominent Auckland prosecutor Vincent Meredith (who was later to become involved in the case) was to point out in another context, it was extremely difficult to prove that someone had been murdered with veronal because 'veronal could be bought freely [at least before 1 April 1935] and it was impossible to establish that the deceased had not himself had veronal and self-administered it'.²⁵ Indeed, in 1933 there had been another famous criminal trial in Auckland where a nurse, Elspeth Kerr (who would today be a clear candidate for a diagnosis of Munchausen's Syndrome by Proxy), was accused of attempting to murder her adopted daughter with veronal. Although there was clear evidence that the only way in which the child could have taken veronal was through the auspices of her mother, the juries in Kerr's first two trials could not agree. It was only after she had endured a third trial that she was convicted of attempted murder. Although after investigations by the real-life prototype of Georges Simenon's fictional Inspector Maigret, the young Parisian woman Violette Noziere, who killed her father with veronal in 1934 (after he had lain in a coma for about thirty page 43hours), was convicted of murder and sentenced to the guillotine, no one living under British law had ever been convicted of murdering someone with veronal. Thus O'Leary (who was unlikely to have known of the Noziere case) could inform the jury that 'a conviction of murder… would make history'.²⁶

As far as the medical evidence was concerned, there were three main questions.

Firstly, how much veronal had Thelma consumed over the weekend? This was crucial because O'Leary raised the possibility that Thelma might have been 'susceptible' to the drug and therefore killed by a relatively 'normal' dose. Obviously, it is unlikely that a man such as Mareo, used to taking the drug frequently, could have intended to murder her with a 'normal' dose. One of the Crown's three doctors, Dr Gunson, denied that Thelma displayed the symptoms of a 'susceptible' patient suffering from veronal poisoning, but he neither explained why a normal dose for a susceptible person did not produce the same symptoms as an overdose for a normal person, nor described how susceptible patients behaved after they had taken a medicinal dose.²⁷ Nevertheless, on the authority of the overseas expert toxicologist, Sir William Willcox, all three doctors agreed that Thelma had taken a total of about 100 grains of veronal. The authority of Sir William was crucial because Thelma's body did not contain all the veronal, unknown amounts having been excreted in her urine both before her final period of sleep and later on a nightdress that had been washed either by Stark (according to Brownlee) or by Brownlee (according to Stark). However, O'Leary was able to point out to the doctor who had conducted the post-mortem, Dr Gilmour, that

Sir W. Willcox was unable to say how much veronal was taken in those cases [of veronal poisoning to which Dr. Gilmour had been referring] – It isn't recorded [conceded Gilmour]. Q. If it had been obtained it would have been recorded? – In one case he says 'probably about 100 gr. were taken'… Q. That is the only case in which there is an estimate of the amount taken? – The only fatal case in this series.²⁸

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Somewhat later Dr Gunson also admitted that he could not say why Sir William had estimated the amount of veronal in only one fatal case. Clearly, the Crown's doctors were considerably more certain than the authority upon whom they relied.

Secondly, how much veronal was in the milk and was it the fatal dose? As we have seen, Stark testified that Thelma drank at least half the cup of milk without the aid of a spoon. In contrast, Graham claimed that Thelma did not drink directly from the cup and drank '[o]nly a very little' from several attempts to give her the milk from a spoon.²⁹ Since a few spoonfuls of milk could not have contained a fatal amount of veronal (due to its lack of solubility), Thelma could not have been given a fatal dose if Graham's testimony is to be believed. Thus Dr Gilmour testified that at the preliminary inquiry he had formed the opinion on the basis only of Graham's evidence that it was 'impossible to say' that the last dose of veronal was in the milk. O'Leary then asked:

In this Court you are in the same position with regard to the evidence except that you read Graham Mareo's evidence? – Yes. Q. Are you in any better position to form an opinion as to whether the last dose was taken in the milk? – No. Q. Worse I suggest? – Yes, possibly. Q. Why worse? – Based on the estimate of the quantity of milk taken.³⁰

Thirdly, was any veronal in the milk at all? The evidence that it was in the milk was completely circumstantial and therefore based on the principle allegedly derived from Sir William Willcox that someone could not relapse back into a coma without a further dose of veronal. However, according to Dr Ludbrook, Thelma was not even initially in a coma but 'sleeping naturally', albeit from what O'Leary described and he agreed was a 'slight overdose of veronal'.³¹ But even if she had initially been in a coma, it is by no means clear that she ever came out of this coma before taking the milk. O'Leary had discovered a case of veronal poisoning documented by a Dr Durrant in which a man had roused from an apparent coma, page 45been able to take liquids only by a teaspoon, and then relapsed back into a coma from which he never recovered. Dr Gilmour maintained that this case did not apply to Thelma's because '[h]e could be roused by effort—but not of his own accord'.³² However, Thelma only roused of her own accord according to Stark's evidence. Although Stark testified that Thelma had called out just before Graham went to the Dispensary for the sal volatile, Graham said, 'I didn't hear her.'³³ Stark maintained that Thelma chewed and swallowed the bread whereas Graham remembered that '[t]hey forced a bit in between her teeth but I don't know if she swallowed it'.³⁴ Furthermore there was the following exchange between O'Leary and Graham:

During the time that you were giving her the milk wasn't it that she was just trying to go off to sleep — Yes. Q. And she had to be roused when the attempt was made? – Yes. Q. She couldn't sit up herself and take it? – No.³⁵

But the really telling evidence that veronal may not have been in the milk was the never disputed fact that Thelma began to fall back to sleep or relapse back into a coma while she was being given the milk (according to Graham) or immediately afterwards (according to Stark). O'Leary asked Dr Gilmour:

[t]he evidence was that she went back into the coma within five minutes of the administration of the milk? – Yes. Q. If that coma was induced by a… dose of veronal that dose must have been administered by an earlier dose of veronal? – All I can say is… [ellipses not ours!] Q. It couldn't have been administered in the milk — if those facts are correct? – If it is correct that she was slipping into a coma at the time the milk was administered then in that case the veronal could not have been in the milk. [our emphasis].³⁶

Although Dr Gilmour would later qualify this testimony by saying that for a variety of reasons the veronal would have been 'absorbed with great rapidity', he did not confirm that its absorption must have been — as Stark's evidence suggests – page 46virtually instantaneous. Instead, he told the court that 'I think my point was that it must have been given within half an hour of her going to sleep'³⁷ – which means that it may have been taken before the milk.