Why was the sinking of the lusitania a turning point for americans who had recently been in favor of neutrality?

The sinking of the Lusitania was a turning point for several Americans. This British ship (that had American passengers on it) was sank by a German submarine during World War I. Over 100 Americans were killed in this attack. This angered the American citizens, as it was rumored that the Lusitania did not have any weapons or military equipment on it (even though it did). Americans saw this as a vicious attack and changed their view on the war, as they now saw Germany as an enemy who was trying to harm innocent American citizens.