Like all conspiracy theorists Walter starts from the wrong end
IF someone wanted to kill these guys they could take them out, one at a time, by taking a bus ride top their houses and shooting them at the their front door (God knows it happened often enough) instead
Why wait until they were all on a helicopter and take them out that way? The complexities are mind boggling and neither MI6 nor the Provos ever showed a real ability to plan and carry out seriously complex operations