Complex sentence: However, the first (and only) call to the fire department was made at 3:42 a.m. by the night manager, who was reported to have attempted to warn guests by telephone of the fire.
Split into simpler sentences: However, the first (and only) call to the fire department was made at 3:42 a.m. by the night manager. The night manager was reported to have attempted to warn guests by telephone of the fire.