Ep 21. Up in Smoke

When an elderly couple died in a suspicious house fire, their son became the number one suspect. The son urged his innocence; he said he tried to extinguish the fire by pouring water on it, but that only made it worse. Investigators turned to forensic science to determine if the fire had been set on purpose, or if it was truly an unfortunate accident. Originally aired as Season 10, Episode 4.