The martyrdom of James (grey) and his accuser (white)
The Catholic Church holds that those who profess Christ but do not yet receive the sacrament of baptism nevertheless receive all the benefits and grace of baptism through martyrdom. This is the teaching baptism by blood which has been held by all the doctors of the Church.
Tradition relates that Saint James’ martyrdom is the origin of the Catholic understanding of “baptism by blood.” The accuser of the Apostle James was so moved by James humility that he was touched by divine grace and desired to die alongside James as a disciple of Jesus Christ. This man received martyrdom along with James the Apostle and the accuser was declared “baptized by blood” and thereby saved and holy.
I may be wrong, but this would have been the first Apostolic recognition of “baptism by blood.”