A shooting at the Chabad synagogue near San Diego on Saturday left three people injured and one woman killed. Police are holding a 19-year-old man after identifying himself as the shooter. Police say he wrote a nine-page anti-Semitic manifesto. The attack came a week after coordinated bombings killed more than 250 people in hotels and churches in Sri Lanka. In March, 50 people were killed in two shootings at a mosque in Christchurch, New Zealand. Synagogues, churches and islamic centers have boosted security in response to these attacks. Some have even started conducting active shooter drills.