October 27, 2018, began as a peaceful Saturday morning. It was the Sabbath many of the residents of Pittsburgh's Squirrel Hill neighborhood, and there was a slight drizzle as they made their way to synagogue. The tree-lined neighborhood about 10 minutes from downtown Pittsburgh is a hub of the city's Jewish community, and one of the largest predominantly Jewish neighborhoods in the country.

A profound sense of security reigned in Squirrel Hill, which is home to a dozen synagogues, including the Tree of Life Synagogue, where a killer waited outside.