In Norway, it appears, such things happened quite often and documents about the legal proceedings following such killings survive. A number of these were discussed a few years ago in a fascinating book by Olav Solberg, Forteljingar om drap. These and many other medieval documents, published in the multi-volume Diplomatarium Norvegicum, were most usefully digitised some years ago in an initiative to make work for those who objected on grounds of conscience to taking part in Norway's compulsory military service (!). These documents are a fascinating and inexhaustible resource for all kinds of historical enquiries. In my search for things that happened at jól I found the following intriguing but sorry tale.
The first witnesses were a couple who swore a solemn oath on the Bible that the perpetrator had announced to them that he, Tore Håvardsson, had stabbed Tore Stavn at Hattrem. This is more like the Icelandic sagas than our modern detective stories, since there is no question about who the perpetrator is. It was important to announce yourself as the killer since then it was drap 'killing' and not the much more serious crime of morð 'murder'. Indeed, the investigator makes clear from the beginning that the death was 'unintended'. Other witnesses then swore solemn oaths as to what had happened. Apparently a group of men had started their drinking at the farm of Hågå on the evening of Christmas Day, and had been to another farm as well, before they ended up at Hattrem, where they would have been well plastered by the 28th. There is an amusing interlude during which the victim lay down in bed, fully clothed, and refused to go when the perpetrator wanted them all to go back home. Tore Håvardsson may have become a bit tetchy as a result and then for reasons not explained got into a fight with another person present. Tore Stavn got himself stabbed when he woke from his drunken slumber and tried to intervene.
Another document from a few years later tells what the result of these official investigations was. Because the crime was unintentional, Tore Håvardsson got off with the usual pair of fines, known as tegn oc fridkiøp, both payments to the king, the first for having killed one of his subjects and the second to buy his freedom. He probably also had to make a payment to the victim's family, though no document survives recording this.