Authorities are investigating the social media posts made by the suspected gunman in a California festival shooting that killed three people and injured more than a dozen others in an effort to determine a motive in the attack. Gunshots rang out Sunday just before 6 p.m. local time at the popular Gilroy Garlic Festival in the city of Gilroy, some 80 miles southeast of San Francisco. Santino William Legan, 19, was identified as the alleged shooter on Monday, law enforcement sources confirmed to ABC News.