The gunman confessed to officers while he was surrendering and later explained that he had been targeting Mexicans.
During the investigation, the suspect said that he had used an AK-47-style gun and brought multiple magazines containing ammunition from Texas to carry out the mass shooting, Garcia wrote in the affidavit.
Titled "The Inconvenient Truth", his message railed against the dangers of mass immigration and warned that Hispanics will eventually take over the economy and government.
"The fund is working with the County of El Paso and the City of El Paso to aid affected families", the team said in a statement shared on their official Twitter page, alongside a link where fans could join them in giving a donation.
Prior to carrying out the attack on Saturday, Crusius published a white supremacist manifesto online which expressed fears of a "Hispanic invasion" of Texas.
Crusius has been charged with capital murder and is being held without bond.
8 out of the 22 people that were killed in the El Paso shooting were Mexicans. Federal prosecutors have said they are also considering hate-crime charges.
O'Rouke, a former USA congressman who represented a district that includes El Paso, joined more than 100 people in the march, which began at a park and ended at a courthouse, across the street from the jail where Crusius is held.
Jessica Coca Garcia, who was among those wounded in the shooting, spoke to those gathered at the League of United Latin American Citizens' "March for a United America".
Democratic presidential candidate Beto O'Rourke on Thursday crossed into Mexico for the funeral of one of the country's victims.
Trump said that there is no justification for the killing of innocent people. The FBI has labeled two of those attacks, at the Texas Walmart and California food festival, as domestic terrorism - acts meant to intimidate or coerce a civilian population and affect government policy.
The two incidents have prompted a national debate about gun laws, with Republicans indicating they may be open to tightening background checks on buyers.