If you speak Spanish, you can learn more about the 1932 massacre known as La Matanza by watching the documentary film 1932, Scar of the Memory which is available for viewing over the internet at this link.
The documentary is from the Museo de la Palabra y la Imagen, the Museum of the Word and the Image. From the museum's web site:
The Museum of the Word and the Image (MUWI) is a privately funded, legally established non-profit organization, dedicated to investigating, rescuing, preserving, and presenting to the pubilc elements of the culture and history of El Salvador.
It possesses collections of manuscripts, photographs, audio recordings, films, videos, posters, objects, and publications, donated to the museum through the enthusiastic collaboration of the society that has responded to the call “against the chaos of amnesia.” Since 2004, the MUWI has preserved and shown to the public “The Legacy of Salarrué.”
This important heritage, previously in danger of disappearing, is being classified, and progress is being made toward its digitization.
Permanently located in the capital, the MUWI brings temporary expositions centered on themes of identity, culture, and historic memory to the most isolated regions of the country. Additionally, the MUWI produces books, audiovisual projects, and numerous educational and cultural activities.
You can also purchase an English-language version of 1932, Scar of the Memory from the museum's online store.