Our knowledge of Late Roman law is biased by a “top-down” perspective: we tend have a good knowledge of how it worked at the top (in the imperial court), and a poor knowledge of provincial/vulgar law; but I can try to give you a few leads. In this case, you would probably be arrested by bucellarii, members of a private militia in the service of an important private landowner (especially if you are a tenant farmer on his lands, something that is statistically likely in the West). Their reputation is, to say the least, not ideal; you may get beaten in the process. Then, you might be detained for a while in an estate jail ran by the dominant aristocratic family of your region. Given the gravity of your act, the case is likely to be deferred to the provincial court. I don't really know who is likely to be there; probably a specialist of the law (assessor) and the governor (the reduction of the size of provinces in the Late Roman Empire allowed for a greater investment of this kind of micro-management). In the mean time, you are likely to have been tortured. In terms of sentence, you can expect the death penalty, and the confiscation of your belongings. You would be allowed to appeal if the evidence against you is not entirely clear; otherwise, if you have confessed, or if the testimony of witnesses is consistent enough, legal proceedings would stop at this point, and the sentence would be quickly carried out.