The charges stem from the Sept. 11 fire that destroyed Victory Baptist Church, along with a fire set Sept. 4 on the same property.
Diaz — who was arrested Sunday — was ordered to remain jailed in lieu of $150,000 bail.
The blaze was reported at 2:22 a.m. Sept. 11 at the two-story church at 4802 S. McKinley Ave., according to the Los Angeles Fire Department.
"LAFD arson investigators and the multi-agency House of Worship Arson Task Force initiated an investigation into the fire's cause," according to a department statement. "Initial information did not immediately reveal any evidence of an intentionally set fire; however, their persistence later uncovered security footage to help connect the dots."
PREVIOUS COVERAGE: Historic South LA church destroyed by fire
The joint investigation included personnel from the Los Angeles School Police Department and the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives. Investigators were aided by eyewitnesses, the LAFD reported.
About 150 firefighters were sent to the fire scene, according to Nicholas Prange of the LAFD.
"Crews initially made entry to find heavy smoke inside the structure," Prange said. "As firefighters made entry, inevitably introducing more air to the conditions inside, fire behavior worsened quickly. Approximately 30 minutes after the arrival of firefighters, there was a structural collapse inside, trapping several LAFD members."
Two mayday calls were sent out over the radio for trapped personnel, and nearby crews quickly rescued three firefighters, officials said. One was taken to a hospital in moderate condition, a second finished battling the fire and was later hospitalized in fair condition, and a third followed up with care on his own after the fire, Prange said.
After the collapse inside the building, crews withdrew into defensive operations, pouring water onto the flames from outside the building. The fire was extinguished in an hour and 40 minutes, Prange said.
Victory Baptist Church was a spiritual center of Los Angeles' Black community for decades, and a site of major significance for gospel music and the civil rights movement. The church was founded by Arthur Atlas Peters on Easter Sunday in 1943, and moved into the McKinley Avenue building in 1944.
Pastor W. Edward Jenkins has vowed that the church will not fold its tent.
"A church is a sanctuary, a place of worship, a place to heal and most of all a place to come together for the betterment of the community. The fire at the historic Victory Baptist Church deeply wounded our community," District Attorney George Gascón said in a statement announcing the charges that were filed Sept. 15. "It was heartening to hear that the leaders of Victory Baptist are looking to rebuild this institution where the Rev. Martin Luther King Jr. once preached and gospel great Mahalia Jackson sang. I'm confident that Victory Baptist will continue to be a beacon of hope in South Los Angeles."