Cedar Falls Mayor Rob Green confirmed the deaths in a Facebook post.
"This morning, our neighbor and Cedar Falls Public Library employee Sarah Schmidt, along with her husband Tyler, and daughter Lula lost their lives to a 23-year-old gunman who then took his own life," Green wrote. "Details will be forthcoming about services and other memorials, and I will ensure the community knows about this. Please offer some extra grace to the Schmidts' many friends, neighbors, and coworkers as we try to process this horrible tragedy."
Green released another statement sharing a GoFundMe page in support of Arlo. More than $220,000 has been raised to date.
A relative who created the page in support of Arlo wrote, "Arlo is a strong boy, surrounded by family and friends who are supporting him as best we can."