There are plenty of synonyms in English for thieves. I'm looking for a word or expression that describes people who rob dead bodies on the battlefield.
In the novel Les Misérables, by Hugo, Mr. Thenardier robs dead bodies in the aftermath of the battle of Waterloo.
The 1949 Geneva Convention Article 18 contains this paragraph:
After each engagement, Parties to the conflict shall, without delay, take all possible measures to search for and collect the shipwrecked, wounded and sick, to protect them against pillage and ill-treatment, to ensure their adequate care, and to search for the dead and prevent their being despoiled.
So we could have "despoiler". Merriam-Webster defines despoil as follows:
: to strip of belongings, possessions, or value : PILLAGE
There is also "marauder" for people who roam a battlefield robbing the dead and wounded. It is referenced in the ICRC War Crime definitions.
Obviously, there are "grave robbers," people who steal possessions (and/or the bodies themselves) from people's graves, but that's not quite the same thing.
A catch-all legal term for such theft is "estate looting," one who performs such looting being an "estate looter." This would apply because if the stolen items had been left on the bodies, they'd belong to that person's estate, go to that person's heirs or next of kin. But that's a catch-all term, not one specifically related to the battlefield.
In the vein of "looter," another term I've heard in the context of the Battle of Gallipoli is "body looter." While I couldn't find those examples, I did find others where it's used in battle contexts:
"Tiredness gnawed at him; he cared little for the body looter, but as he turned back towards the streets a window shattered amidst a woman's screams..." -Master of War by David Gilman
"He looks for his watch and then he remembers the body looter who was taking it off his wrist when he was lying in the field." -The Window at St.Catherine's by John Dobbertin Jr.
"I’d been in the Golden Horn before: with Cal, on jaunts to recover a young fallen before the body-looters got at him. As O’Connor and I walked past the dilapidated buildings, I felt Cal’s absence all the more keenly—and it wasn’t a body-looter..." -"The Inaccessability of Heaven" by Aliette de Bodard
"He saw his enemy standing over him with his wrist-watch in his hand... "So you are a body looter as well," he said; "you rob the fallen." -The Lion and the Adder: A Story of the South African Rebellion by Leigh Thompson
(In the second example and the fourth example above, each does refer to taking from the dead, the given subject "he" being a different male than the male that "his" refers to, each account being a male soldier speaking of another male soldier who is deaceased and a belonging of that other male soldier who is deceased, which, by coincidence, in both cases is a watch. That said, I'm not sure there's much distinction betweeen stealing from a soldier who isn't yet dead or who is too gravely wounded to be conscious or to prevent the the theft but ends up surviving, so I would imagine the term may be able to apply in those cases, too, though I don't have any examples to support that. On the other hand, maybe not as "body" in such contexts is rather suggestive of being deceased.)
While a Google search shows "body looter" is used mostly in war and battlefield situations, there is a spattering of examples where it's used in other contexts, but given how the preponderance of its usage appears in battlefield situations, it very well could be that it's battlefield term or a term born on the battlefield but has been appropriated for use in those other contexts. I can't say for sure because I can't find any etymology or really any research at all on the term "body looter," just a plethora of examples of its usage.
Scavenger is the term for someone who loots dead bodies (corpses), especially on a battlefield. The phrase human scavenger is used also. It is an allusion to the extended sense of scavenger: an animal (like a vulture) that feeds on dead organisms (carrion). It is also related to the various figurative uses of scavenger: someone who collects things discarded by others, someone who does ‘dirty work’, a dishonourable person etc.
The term scavenger is even used in an English version of Les Misérables, for the villanous character Thénardier who loots corpses:
We encounter Thenardier, a human scavenger, robbing corpses in the aftermath of the battle of Waterloo, and amassing enough loot to set himself up as an innkeeper.
Les Misérables: TV tie-in edition by Victor Hugo
I've also found the term used in a book about the American Civil War:
The report of Provost Marshal Marsena Patrick noted angrily that one organized effort at stealing involved “a number of nondescript scavengers” who made money by selling rags to a paper mill. They came in teams, day and night, to loot dead soldiers.
The Aftermath of Battle: The Burial of the Civil War Dead By Meg Groeling
Scavenger is the term used in gaming jargon also, as corpse looting is a common practice in video games. Here is the description of a scavenger from one of the most popular role-playing video games, The Elder Scrolls V: Skyrim:
Scavengers are hostile enemies that appear in The Elder Scrolls V: Skyrim. They roam Skyrim looting the bodies of dead people and animals alike. Scavengers usually are found searching the bodies of soldiers that fought in the Civil War, such as Imperials and Stormcloaks.
elderscrolls.fandom.com
Based on @eirikdaude's advice to look in an English edition of Les Misérables, we go to Volume 2, Book 1, "CHAPTER XIX—THE BATTLE-FIELD AT NIGHT" and find that the term "marauders" is indeed used:
The marauders stole in one corner of the battlefield while others were being shot in another.
This lines up with @SpehroPefhany's answer (although I agree that it doesn't have that specific connotation in modern English).
Thénardier is also described as a "nocturnal prowler" (although that's not specific to battlefield scavenging) and as a "ghoul" (which could be a useful metaphorical description, although again non-specific).
You could use the word pillage or pillager:
the act of looting or plundering especially in war
to rob of goods or valuables by open force, as in war, hostile raids, brigandage, etc.
