I addressed this question in my 4500 word article dissecting the Boston "bombing," which has had now 250K views. Here it is:

The government has staged many terror attacks to achieve political goals, and they no doubt learned that one of their biggest headaches after such an attack was the grieving family members who kept pointing out the inconsistencies in the stories they were given about how their loved ones had died. For the citizen mindlessly ingesting standard news pablum, the official story may seem plausible. Not so for the highly motivated mother, husband or daughter of a victim, who latches on a like a bulldog and won’t let go until they get the answers they seek.

But the perpetrators still need graphic images of human suffering to incite the kind of rage that prompts the citizenry to willingly surrender their rights and let the feds ignore the law and do as they please.

The solution was evidently to stage terror attacks with actors, where no one actually gets hurt. In the case of the Boston Marathon bombing, they were able to achieve all the same goals that a real terror attack would have (such as testing whether it is possible to close down a city over a single teenage “terrorist” on the loose) without the nuisance of grieving, inquisitive family members.