Saudi Arabia's King Salman has ordered a safety review of the annual Muslim pilgrimage after more than 700 people died in a fatal crush on their way to the holy sites of Mecca.

It's the worst tragedy at the hajj in 25 years and looks as though it occurred when two massive groups of pilgrims converged from different directions onto one road.

Crowd-control experts believe victims in the crowd were more likely to have died of compressive suffocation, rather than a "stampede." Abdullah Lotfy of Egypt told the Associated Press, "People were climbing over one another just to breathe... It was like a wave.

You go forward and suddenly you go back." The kingdom of Saudi Arabia has spent billions of dollars to accommodate the growing number of pilgrims, but critics say better management of the event could have prevented yesterday's tragedy.

It's the second major accident during this year's hajj season. On September 11, a construction crane crashed down onto the Grand Mosque, killing 111 people and injuring up to 400 more. The hajj draws 2-million people annually. Who can be held accountable for the deaths of the pilgrims? What will change before next year's pilgrimage? Will Muslims fear attending the hajj going forward?

Guests:

G. Keith Still, Professor of Crowd Science (Crowd Risk Analysis) at Manchester Metropolitan University in Manchester, England

Anisa Mehdi, Journalist and filmmaker who has covered the Hajj since 1998 and produced two films about the pilgrimage for PBS and National Geographic