The year is 1320, I am a peasant living in Central Europe. During the night, masked men enter my house, assault me and steal the little money I have and some other goods. To whom do I report the theft and what kind of investigation would take place?

If you're a peasant in later medieval Germany being attacked, robbed, and burned out, chances are you know exactly who it is even if you don't know who the people are. It's probably a raiding party from a local knight, and you're probably caught in a feud between two of them.

It was no fun to be a peasant caught in any kind of warfare between nobles or kingdoms; the English chevauchees in France during part of the Hundred Years' War being the most notorious but far from the only examples. However, feuds--and the problem was especially rife in the Holy Roman Empire--were a particular form of ongoing enmity and violence between members of the lower nobility in which targeting one's own peasants and the peasants of the enemy was a well-worn tactic.

You can think of a feud in the sense of an "honor battle," in which one party claims to have had their honor attacked over a spurned marriage, or castle built on the other's territory, or some such. But often, as Hillay Zmora showed, events like this were more pretext than actual cause. Feuds were about lower-level lords jockeying for power not only between each other but in the eyes of the higher nobility and princes, perhaps even the emperor. And in Zmora's words, peasants were both "objects of" and "pawn in" these vicious games.

On one level, the point was straightforward ruination of the property of the feuder's opponent. Chronicle accounts of one Franconian feud in the fifteenth century mention parties shooting not just sheep flocks but shepherds with arrows, firing cannonballs at small towns, burned villages and crops, destroyed local resources like fishponds and patches of forest.

A second purpose of attacking peasants--the robber knight's own, or their opponent's--was fear. They wanted to terrorize peasants into essentially doing whatever they wanted in terms of paying tribute to them, not paying taxes to the opponent, providing labor for castle-building, and so forth.

And third, to attack peasants in a village belonging to one's enemy was psychological warfare against the noble (screw the peasants; who cares about them). A feud between the city of Nuremberg and a nearby robber knight at the end of the 15th century saw Schott's men raid a village--but not the village proper; the hideout where villagers fled upon their approach. The attackers apparently had brought some women (I am not aware of more specific details) along with them to pretend to act as negotiators/friendly faces. One peasant stepped out to talk; the attackers promptly shot him full of arrows. According to a contemporary pamphlet describing the feud's course, one of the arrows was engraved "For a Nuremberger." The point was to attack the city (city's leadership). Peasants were pawns.

In medieval Europe, peasants did have the right to appeal bad treatment. Villages might send delegations to one of the robber knights involved in the feud demanding protection; they could appeal to the duke of the larger territory (or territories) in which the feuding knights held their land and castles; they could try appealing to the Church via the episcopate. (Of course, sometimes one of the feuding parties was the Church, in the form of a bishop-lord, and the appeal would be pretty much DOA. Studying twelfth century violence, Thomas Bisson found exactly one case of the Church willing to censure and punish its own for feuding tactics like murder and arson).

Would it work, though? Ehhhh.

There are, of course, plenty of cases where the attackers were more what OP probably has in mind--local bandits or outlaws out to steal or just to be violent. An ongoing feud (or larger war) could even abet this kind of behavior, as outlaw gangs were more likely to be active (and more likely to be able to stay active, that is, not dead) during periods of chaos.

Strictly speaking, territories in the Holy Roman Empire did have officials responsible for preventing these attacks and catching offenders. Unlike France and England, German territories did not have standard official courts set up to prosecute such offenders, so a town mayor or lord's delegate is probably who stepped in. But first the bad guys had to be caught. And, frankly, the designated/hired officials were terrible at their job.

Some of it wasn't their fault. Leonberg had 1000 inhabitants, one constable, and two watchmen. And typically, constables and watchmen were also responsible for basic community policing (in early modern Germany, a bit later than OP's frame of interest, this included things like making sure wedding celebrations didn't get out of order). So you can imagine how popular constables were. (With watchmen, there was another problem--Gerald Strauss explains how late medieval Nurembergers despised how noisy the watchmen were at night, always calling out to each other.)

Where constables tended to have more success wasn't interrupting in-progress attacks or catching offenders of specific robberies, murders, and acts of arson. Instead, it was general territorial managements--rooting out bandits of any kind in their hideouts in other villages, forests, and so forth. Villages could organize posses to go on the hunt like this, too. That seems to be what happened in the case of a cluster of Hungarian villages in 1493 dispatching the Glowaty brothers' outlaw gang step-by-step, one or two imprisonments and hangings at a time.

For on the spot action, there was one major recourse: the Notruf ("hue and cry" is the phrase you probably know) and mob justice. You may be familiar with the idea/legal principle that in order for a rape to be considered rape, the woman attacked had to raise a hue and cry immediately. (Now imagine how traumatized she was, and possibly injured, and definitely going to face significant shame from people who thought she was a slut who wanted it/asked for it anyway, and how much further trauma that might cause).

But the Notruf wasn't only to catch rapists, of course. In fourteenth-century Germany, in fact, it was often a brutal anti-Semitic tool. Not just in fictionalized or outright fictional sermon exempla but in actual, chronicle and court-recorded situations, the Eucharist Host (bread) or some such would not be where it was supposed to be in a church. The priest who couldn't find it started shouting and knocking on doors and getting people fired up (in exempla/miracle stories, the missing Host itself cries out), and if the town or a nearby town had a Jewish community, you have the fixings for a pogrom.

This is what happened in 1322 Ehingen, when blame decided to focus on a local Jewish woman and Christians murdered eighteen Jews in retaliation. Supposedly, a few Christian women later overheard one of their own admit to the deed/she let it slip in conversation, they reported it to the local bailiff, and the gulty Christian woman was arrested and burned at the stake.

This is a little fishy, though--she allegedly stole the Host to perform a magic ritual of some sort or to sell it to local Jewish people for them to destroy, both of which are utterly stock tropes in Eucharistic exempla. However, the offered route of discovery--overheard or directly repeated gossip--is a good example of what Ulinka Rublack shows was a very common way criminals were caught and punished.

In the case of Ehingen, of course, only after eighteen innocent people were murdered.

Overall, you could say that the best possibility among very poor options for defense was an offense--but that by no means made it a good offense.