In the wake of the Boston Marathon bombings, Americans are asking: How could this have happened?

What about the hundreds of billions of dollars spent since Sept. 11 on counterterrorism efforts? Have they made us safer?

In Top Secret America – 9/11 to the Boston Bombings, Pulitzer Prize-winning reporter Dana Priest investigates a top-secret world that, she writes, “has become so large, so unwieldy and so secretive that no one knows how much money it costs, how many people it employs, how many programs exist within it or exactly how many agencies do the same work.”

The film is based on Dana’s reporting with William Arkin for their 2010 “Top Secret America” series in the Washington Post, which took two years to report and over a dozen journalists to complete.

How do you investigate a world the government doesn’t want you to see? What, exactly, is Top Secret America spending so much money on behind closed doors? And is it making us any safer? How would we even know?

We’ve asked Dana Priest to join us in a live chat to answer those questions — and take yours.  She’ll be joined by Mike Wiser, one of the film’s producers, and by our special guest questioner and panelist Kevin Cullen, a columnist at The Boston Globe who recently wrote a series of columns on the Boston bombings and national security.

We’d like to thank The Boston Globe and The Washington Post for partnering with us on this chat.

You can leave a question in the chat window below, and come by at 2 p.m. ET on May 1 to join the live discussion.