1. You have a collection of black holes that formed from stars in a very dense cluster at the nucleus of the Galaxy early in its life that all merged to form an intermediate mass black hole, which then grew into a SMBH.
2. An intermediate mass black hole formed directly from the direct collapse of a large gas cloud and then grew into a SMBH.
But even the better known case of the formation of stellar mass black holes is still not well understood!
Based on my limited understanding of cosmology, wouldn't the gas first form a star, and not form a SMBH until the star's nuclear reaction became too weak?