Presumption (The normal)
“Had the Jack the Ripper murders taken place in 1988 and not 1888 then our response to them would have been markedly different. No one in 1988 would have doubted that the perpetrator was a sexual serial killer carrying out his own perverted agenda.”
The second sentence of this quote: the one beginning with “No one” is a bit reaching. Maybe a majority of people would not have doubted what Jack the Ripper was, but an all reaching statement like this based on what is really just speculation takes away from the author’s argument.
“His early childhood was horrendous…(elaboration on bad childhood)...
The childhood fashioned the adult. The William Bury whom we encounter in Wolverhampton in the 1870's and 80's was a thief, liar and a fantasist prone to sudden squalls of destructive rage.”
The author is saying that because Bury’s childhood was bad, he turned out to be a serial killer. It’s kind of grasping for straws because a lot of people have bad childhoods and turn out to be fine adults, but it’s an argument.
“In their book Sexual Homicide, John Douglas and Robert Ressler, pioneers of psychological profiling and formerly heads of the FBI's Investigative Support unit, present the case of Warren (1), an Alabama multicide whom they use as a 'motivational model'. When Warren's history is compared with Bury's the similarities are uncanny. So too are the parallels between Bury and Fred West. But Bury was obviously not copying Warren or West; instead their lives imitate his.”
Here the author establishes that Bury’s psychological profile was a lot like those of two other notable serial killers. That is, he’s basically saying “B and C are bad. A is, in a way, like B and C. Therefore A is bad.”
“The police also discovered Bury had been a horse meat butcher, cutting the meat up for cats' food. Although not a necessity, possession of the sort of anatomical knowledge a man might gain from cutting up animals is certainly not a disadvantage in the Ripper stakes. John Douglas remarks that employment as a butcher would have nourished the Ripper's sadistic fantasies.”
The fact that Bury was a horse meat butcher isn’t relevant in many cases aside from the process of building an argument accusing him of being Jack the Ripper. More relevance is added through the mentioning of John Douglas’ analysis.