The black bag

[Meet Ze Monster]

I'm gonna go out on a limb and suggest that JtR's weapon was very likely a tool of his trade (it would arouse less suspicion if by chance he was seen with it).
If it was, then was it a medical tool? I could be convinced of his knowledge of anatomy by the sheer speed and accuracy he demonstrated in pitch darkness. Looking up images of post mortem knives, some fit the estimated length and width of the killer's blade. I'm not sold on the pen knife thing. Those are not much bigger than a typical pocket knife.

As an aside, what would be interesting to know is, how common was it for men to carry some form of knife about their person (for self-defence) in Victorian London?

[GBinOz]

Imo from what Bond said the knife JtR used probably looked something like this one which is an amputation knife from a museum and was made around 1880 by Weiss.

This type of knife was called a Liston knife, after its inventor, Robert Liston. It was double edged and was used in a stabbing motion followed by drawing up the blade and cutting from the underside with the top edge. Robert Liston was said to have carried his knife up his sleeve, presumably in a purpose designed lining.

Cheers, George

[Losmandris]

I am not sure about the bag? I presume that he must have needed two hands to subdue his victims. Also that surprise was used to render them unconscious. Where would the bag have been when he was making his move? As for the knife I always imagine that he had it wrapped up in something and then stuffed down his trousers or up a sleeve. The only bag I can consider him having would have been a satchel type thing, over the shoulder. This could have been where he placed his trophies?