I wasn't even aware of the Sri Lankan attack. It likely had grave effects locally, but nearly zero impact worldwide. The 9/11 attacks were more far-reaching because they galvanized the most powerful economy and military into action.
I happen to think @jaredbangerter is right, though. Many if not all terrorist acts in the last several decades (if not couple of centuries) have been false-flag operations -- like the infamous unapproved Operation Northwoods.
That America would even plan such a thing is a chilling testimony to the depths the seemingly honest and upright America can crawl.
For over a decade, I had bought most of the Bush conspiracy theory. But no more! Only last year did I even look into the details. I was appalled at the gullibility of us all!
9/11 was an inside job, pure and simple! If you look at only one fact -- that of the tiny iron spheres found in all samples of the fine, powdery concrete dust -- you can see that something else was going on than the official fiction. The fires were not hot enough to melt steel, but here was evidence that several tons of steel were not only melted, but converted to raw iron and atomized! These can be done in a controlled demolition, especially one using thermate cutter charges -- far quieter than C4 or RDX charges.
If 9/11 was an inside job, then that excludes the assumed patsy (Al Qaeda). In fact, Osama Bin Laden may have been telling the truth that he had nothing to do with 9/11. It takes months to place all the charges needed in all three (3) buildings. And the third building, WTC7 came down at perfect free-fall over most of its collapse. That means practically all of its PE was converted to the KE of acceleration due to gravity! Nothing left to bend or break the many floors of unbroken, unheated steel beams. Nothing left to pulverize the thousands of tons of concrete into a fine, powdery dust. Nothing left to spew that dust as a pyroclastic flow across most of lower Manhattan. And nothing at all to convert any of those steel beams into tiny iron spheres! It's called "conservation of energy."
Bush and friends lied.