The first step is to establish a relationship between the potential, future killer and the rest of society that allows him to place a lower value on the lives of his victims than he does on the completion of his task. This usually involves the imposition of arbitrary cruelty on the trainee during his adolescence, cruelty that is either ignored or shamelessly defended by the majority of the community and by adults in positions of authority. Like so many others who've managed to acquire the attention of the media, this appears to have been the conditioning process imposed upon McVeigh during his adolescence. Read the fourth paragraph of this report and take notice of how familiar it sounds. And before you engage in a chorus of, "I was bullied and I never killed anyone" please remember that this is only the first in a two step process.
The second step is to simply wait until the trainee rationalizes that committing a media worthy act is not only necessary, but worth the risk of losing his freedom or his life. This step usually involves a relatively unbroken record of failure in life that the trainee can reasonably attribute to conditions beyond his control. The lack of opportunity to further one's education, the lack of jobs that pay a living wage, the inability to establish a normal relationship with a woman...the absence of conditions that provide one with a sense of belonging, a sense of purpose, and a sense of security tend to produce some very dangerous individuals.
And Timothy McVeigh appears to have been just such an individual.