captain mark, jason mccay, pablo, and jess mcclean were killed defending a vacant home. >> reporter:t did the world lose when we lost your son? >> danny was a - an amazing son. he loved - loved his work. he was 20 years, 7 months and three days. >> reporter: nearly nine years later and the wound is yet to heel. with the dark day, the news was delivered, forever time. >> it was two gentlemen in forestry uniforms, and i said we have to tell you that your son, daniel, one of the casualties. i completely broke down. the only thing i wanted to do was just hold him. >> reporter: but the fire was no freak accident. the wildfire that extinguished the lives of five firefighters was intentionally set. >> the full resources of the riverside county, the state of california, and the federal government will track down the custody. >> reporter: finding and bringing an arsonist to justice is tough work. >> it's a very, very difficult crime to prove, it is, in fact, the second-most difficult of all to prove behind only sexual abuse. >> journalist and author john mclean wrote the book, "the esperanzo