Complex sentence: On June 17,2015, at the Mother Emanuel AME Church in Charleston, South Carolina, an unknown gunman entered the building and began to fire upon the congregation, which allegedly included the Reverend and state senator Clementa C. Pinckney.
Split into simpler sentences: On June 17,2015, at the Mother Emanuel AME Church in Charleston, South Carolina, an unknown gunman entered the building and began to fire upon the congregation. Those inside allegedly included the Reverend and state senator Clementa C. Pinckney.