And Even More History and Occult Theories about Bo Lankin, Long Lankin, Lammikins, Etc.
Variants include versions of the song (typical of Scotland) where Lankin's motive is provided: he is a mason who was cheated of his pay by the Lord of the house, and so the murders are done out of revenge. There are also versions where other characters, like one or more daughters or additional servants are somehow involved in the crime, usually as innocents who Lankin forces to watch or to reluctantly participate in the crime.
There are some theories as to what the song is about, starting with the name of Lankin. Those who favor the spelling Lambkin tend to say it's a nickname given either to mock him for his quietly bearing the lack of payment, or else that it's an ironic nickname given because of his known violent tendencies. Anne G. Gilchrist in the 1930s wrote about the evolution of the song, and noted that "Lamkin" or "Lammikin" was not necessarily a misspelling of Lambkin, but is a legitimate Flemish name all itself, and might have meant that the murderous mason was supposed to be a foreign workman.
There are some theories, often repeated in spite of the poor evidence for them. One often found in internet results is that Lamkin is supposed to be a leper who is trying to use the blood of the baby to cure his disease. However, the first reason to doubt this is that it seems like Lamkin being a leper looking for blood would be a lot more remarkable than his being a mason or even having no motive at all, and one would thus expect at least some of the surviving versions to have retained this interesting detail. The other reason to doubt it is that there's little evidence baby's blood was ever used as any kind of "folk remedy" for leprosy. (It is mentioned in some high-end medieval medical texts, of a type that commoners wouldn't have access to, and which dealt more with the theory of medicine than its practice. It's more likely some modern academic would be familiar with them, than it would have been for an actual medieval leper to know them.) Finally, the whole notion seems to be based on those versions of the song where Lankin collects the blood in a basin, which is not a consistent element of the story (only Child's F, G, N, O, T, and V have the detail -- a relatively small number of the total) and really it seems like it might be included for no better reason than that "basin" makes a rhyme for the necessary -in endings in the song about Lankin, which also seem to provide his motive for using a pin to draw the blood rather than some more efficient weapon if collecting the blood were his real goal.
Another unlikely, but oft repeated, occult-sounding theory, is that the mason needs to consecrate the house with blood in order to finish the job -- though if he went unpaid, it seems odd that he would be so anxious to do so. To explain this, another story that is never mentioned in the song gets added, that Lankin must have killed his own child to consecrate the house and now wants the Lord's child's blood as payback. But this has the same issues as above (no version of the song retains these details which should be more interesting than mere unpaid wages, this ancient practice wasn't used anymore by medieval times much less the 17th century when the song appears, and it's once again all tied to trying to explain the basin versions of the song.)
It seems more likely than any of these supernatural reasons that the song merely retells some known crime, like the songs of Lady Warriston tell of the actual crime which occurred in the year 1600. Between muddied details of the Lamkin songs (for example, the victim is often said to be Lord Weir or Lord Wearie, but also named variously as Lord Arran, Lord Lauriston, Lord Earie, Lord Montgomery, Lord Murray, etc.) and the sad fact that court and criminal records from so long ago don't always survive, it's very unlikely that the source crime could be identified with certainty.
As far as a true crime basis for Lankin, there is an interesting incident which happened circa 1575 in Scotland. It shares a few common details -- a revenge crime against a Lord and his Lady, creeping in through an open gate with only the Lady and her female servant discovered at home, trying to lure someone out with another person's scream -- though it is not so exact that one could definitely say it's the same crime. I'm including it for general interest.
The incident was some kind of family squabble gone awry: the trouble began when Lady Hessilheid slapped a servant, Robert Kent, belonging to her relative John Montgomery. Kent, John, and his brother Gabriel Montgomery, returned to her house at Hessilheid (also called Hazelhead) early in the morning to avenge themselves, "and" (I'm translating this out of 16th century Scots for you) "finding the gate of the said place open... [found] the said Lady opening a locked bole, and no person with her and no person therein but one girl, the said Robert Kent pulled her down by the hair of her head backward to the ground, and struck and beat her with his fists and feet numerous many grievously painful strikes wherewith they have bruised and broken her bowels that she is never able to conceive children again... meanwhile Gabriel stood with a cocked pistol in his hand, holding the mouth thereof to the door that comes from the proper chamber of the said Hugh [Lord Hessilheid] to the hall, thinking the said Hugh should have come in at the hall door to relieve his said wife when he heard her cry." The malefactors worried they would rouse others with their commotion before they were able to lure Hugh, and they left, stealing some items and one of his horses when they went. Hugh chased after them but was "met with pistols and drawn swords" and after being badly injured was left for dead.
Evidently Hugh retaliated against his relative Gabriel at a later time, and the Hessilheid servants are later found on trial for his murder.
(And the story didn't end there, as Robert Kent was then acquitted of any wrongdoing, but the Assise later tried for "wilful error" or in other words, rigging the verdict. These court cases evidently went on for a time, back and forth, with no actual convictions of anyone.)
I can just hear the rising wail.
"No, Talia! Not more Lamkin! No!"
But yes, alas, it's more Lamkin.
I recently came across a searchable database of English Broadsides (before Youtube, this was how you shared songs, urban legends, gross news and so forth, through broadsides or broadsheets). I began trying to plug in any combinations of words that might lead to early/obscure versions of Lamkin. Some interesting finds:
Contains the phrase "as good a ____ as ever laid stone" as in the older versions of Lankin. Which is odd, because this song is about a miller, who I don't think has a reputation for stone laying? The remainder of the lyrics are about the miller attempting to dupe a woman into sleeping with him in exchange for free flour, but his wife catches on and takes the woman's place in bed.
There is a hint in many versions of Lankin that his real target is some kind of revenge or seduction of the lady of the house, but the connection seems pretty weak beyond perhaps a borrowed line (and perhaps a common tune -- I can't find any version of The Bed's Making.)
There are several broadside songs about Shinkin, apparently being a stereotype Welsh name. It is superficially similar to Lammikin, Lincoln, Bilankin, and other variants. I actually came across this song because of the lyric "with a pin" -- which here Shinkin uses to spur on a goat. He is a criminal committing crimes, though nothing as severe as murder. Mostly just notable as another similar name circulating in ballad tradition.
This is actually the same story as the old Snow White and the Wicked Queen, but without the hunter feeling a last minute pang of conscience that prevents him from going through with the assigned murder. Then, like the old Greek myth of Philomela, the corpse is baked into a pie that is fed to the father.
The connections to the Lankin story are that the crime takes place while the lord of the house is away hunting; and also the fate of the murderers -- "The cruel step-mother/For to be burnt at stake/Likewise he judged the Master Cook/ In boiling oil to stand." There are also some versions of Lankin in which a daughter of the house is present, and either is killed or, like the scullion boy of this tale, attempts to intervene in the murders.