Why did pizarro and his forces attack the inca and capture their emperor, atahualpa?

Pizarro staged a mock trial and found Atahualpa guilty of revolting against the Spanish, practicing idolatry, and murdering Huáscar, his brother. Atahualpa was sentenced to execution by burning. He was horrified, since the Inca believed that the soul would not be able to go on to the afterlife if the body were burned.