Waaay too many people knew about the scheduled cash drop off!
It appears there was an accomplice in the murders. The money was for a martial arts studio that was going to be built.
http://www.dailymail.co.uk/news/article-3090435/Police-identify-man-suspected-killing-CEO-wife-son-DC-mansion-finding-DNA-pizza-crust.html
Really? Who? I missed it.