From an entry on Greg Ellifritz's blog for February 4th:
If you haven’t heard the news, Marcus died last week. He was one of the deepest thinkers in this field, revolutionizing training programs for the Air Marshals and quite a few secret squirrel government agencies during a time when I was still in elementary school. He was a long time friend of mine and was always super supportive of me and my training business. His passing leaves a hole that won’t be filled anytime soon.