Fringe: Season 2, Episode 14

2 - 14: The Bishop Revival

When a select few people are suffocated from the inside out during a wedding, the Fringe Division investigate. After another attack at a coffee shop, Walter believes the toxin the terrorist is using is targeting certain ethnicities in people through their genes. He also discovers that the killer is over 100 years old, and was a Nazi; Walter's father, Robert Bischoff (renamed to Bishop afterwards) was also revealed to be involved in the project during the 1930s. The team find out the next target, where Walter is able to turn the toxin against the killer, killing him; in the end, Olivia and Broyles decides against arresting Walter for the death.