Early image of Christ holding a book

The BBC reports the find of a glass plate in Spain (here). It mentions a 4th century date for this artefact, which may be true or not. The reconstruction is interesting:



The central figure holding the cross is in all likelihood a depiction of Christ, while the two others I would take as the angels present at the resurrection, not unlike the Gospel of Peter. What is interesting though, is that Christ holds a small codex in his hand, while both companions each seem to hold a scroll.