For seven minutes, five Dagestan rebels spoke into a video camera about killing infidels and how the “good deeds” they were doing would absolve them of “700 sins” committed during their lifetimes. Filmed by a Canadian jihadist fighter before he was killed by Russian security forces, the video offers a disturbing glimpse of the fanaticism of the rebels who may have inspired Boston Marathon bomber Tamerlan Tsarnaev. Tsarnaev does not appear in the footage, which was obtained by the National Post. But it was recorded and narrated by William Plotnikov, a Canadian whose alleged links to Tsarnaev are now under...