Considering the format of the two reliefs (rectangular in shape and taller than wider) and their dimensions (slightly less than 1 metre by slightly more than 30 cm.), the few remaining traces seen before us would seem to indicate that we are looking at two lateral scenes from a dismembered altarpiece dedicated to the Passion of Christ that was probably originally "T"-shaped. These reliefs and other scenes would have flanked a larger, central Crucifixion scene.
Iconography for this type of work is normally exclusive, which is why it is highly improbable that any reference or image would have been made referring to St. Pedro. This, in turn, leads to doubts regarding their possibly pertaining to a larger altarpiece, or at least their mismatch as far as the patron saint of the church was concerned.
Be that as it may, their current framework, though inspired by contemporary works such as the triple St. Ann altarpiece in the church of Elgoibar, is not the original since it does not correspond to that used in narrative scenes, but rather to that housing groups of figures.