The raid was precipitated by Brownsville sheriff Robert Shears attacking a Mexican man named Thomas Cabrera and in turn being shot by Cortina.

On September 28, Cortina and a band of men attacked Brownsville with the intention of killing Shears and his associate Adolphus Glavecke.

[1] After the Treaty of Guadalupe Hidalgo, Tejano, or Hispanic Texan, ranchers in southern Texas came into conflict with Anglo-American settlers, who filed specious claims on property, forcing the landowners into the newly introduced American courts to assert their property rights.

Cortina told the sheriff that he knew Cabrera and implored him to stop the beating, to which Shears responded by shouting "What is it to you, you damned Mexican?"

[3] Two hours before dawn on September 28, Cortina led a group of approximately 75 horsemen over the Rio Grande and into Brownsville, with the aim of rescuing Tejano prisoners and killing Shears, as well as rancher Adolphus Glavecke, who was infamous among the Tejanos for trading stolen cattle.

The Cortinistas freed several prisoners, killing jailer Robert Johnson, blacksmith George Morris, who had hidden beneath his house, and William Peter Neale, who was shot after bolting upright in bed when he heard the invading Cortinistas.