(ANSA) - Catania, April 21 - Italian prosecutors believe that two causes contributed to last weekend's migrant-boat disaster in which as many as 900 people may have died, ANSA sources said Tuesday. The first was the movement of migrants aboard the overcrowded boat and the second was a bad manoeuvre by the trafficker at the command that led to a collision with the merchant ship that had been sent to rescue the refugees, the King Jacobs, Catania prosecutors believe, according to ANSA sources.