Here are my thoughts,

Which is more probable:

A single person whether he was a terrorist, government agent or whack job used a REAL bomb at a REAL concert, killing and injuring REAL kids.

or

The government coordinated over 300 "crisis actors", 20 thousand people at the concert, a few hundred local police, a few hundred local EMS and fire personnel, a couple thousand hospital employees, hundreds of taxi drivers to all act out the "FF"

So what is more likely ONE person hired to actually do a real event bit with hidden motives, Or employing at least TEN THOUSAND people who all are keeping the "truth" a secret.