Complex sentence: At the time of the stampede around one million pilgrims had gathered and were marching toward the shrine of the Imam Musa al-Kazim, one of the twelve Shi'a Imams; apparently, rumours of a suicide bomb attack broke out and panic spread.
Split into simpler sentences: At the time of the stampede around one million pilgrims had gathered and were marching toward the shrine of the Imam Musa al-Kazim, one of the twelve Shi'a Imams. Apparently, rumours of a suicide bomb attack broke out and panic spread.