Authorities investigating the California arson attack that killed four firefighters have questioned and released two “persons of interest”, police said today.

Calmer winds helped crews fighting a massive wildfire today that killed four firefighters and critically injured a fifth, while investigators searched for the arsonist who set the blaze roaring through the canyons of Southern California.

FIRE crews yesterday struggled to protect homes from a wind-whipped wildfire that trapped and killed four firefighters in a wall of flames as it raced across almost 38 square miles in southern California.