As Watson is getting Helen released from jail, he speaks with a man named Lestrade. Lestrade was the nearly incompetent police detective in several Sherlock Holmes stories.
Spring-heeled Jack is a real figure from English folklore.
However, except for the tendency for leaping onto rooves, the character bears little resemblance to the "real" Spring-heeled Jack who was more a horror than a killer.
Jack tormented England for almost 70 years from 1837, avoiding capture by leaping onto (or in some cases, over) buildings. There were complaints made about him all over the country, from him harassing and frightening ladies by tearing at their clothes with his claws or breathing blue fire at them, to terrifying army sentries into setting traps by jumping on the roof of the guardhouse.
Spring-heeled Jack was last seen in Liverpool in 1904 jumping from the street to the rooves and away into the night.