Workers behind Russian-linked Facebook Inc. accounts helped organize or finance real-life events before and after the 2016 election, often working directly with U.S. activists and playing both sides of the same hot-button issue—even on the same day.

In July 2016, as outrage swelled over fatal shootings in Dallas and Minneapolis, alleged social-media agitators tied to Russia worked quickly to capitalize on the emotionally charged atmosphere.

Workers...