A public memorial service was held in San Francisco Tuesday, October 16, 2012 for Christopher Stevens, the U.S. ambassador to Libya who was killed along with three other Americans in last month's attack on the U.S. consulate in Benghazi. Meanwhile, Muslims from around the world have embarked upon a letter-writing campaign - which is collecting thousands of condolence messages for the ambassador's family. Mana Rabiee, of VOA's Persian News Network, has more.