I could be wrong but I do not believe that this is a "false flag." I do not believe that this bombing was a government conspiracy. Conspiracies are rare because by their very nature they are almost impossible to keep a lid on. Textbook example: Watergate. Getting caught (which is inevitable) is not worth the risk.
It could have been perpetrated by a domestic terrorist. Left wing terrorists (Earth First and ELF come to mind) have been completely fine with collateral damage in their crimes but they don't have anything like a public attack on civilians in broad daylight to date and it is difficult to imagine them starting to do so now. So-called "right wing" terrorist attacks have almost exclusively followed a pattern of attacking government facilities such as the Murrah building in Oklahoma City or the IRS office in Austin. The one exception that I can think of is Eric Rudolph who bombed the Olympic Park (among other places). That was a soft target. I guess what I'm saying is that the record for domestic terrorists of all political leanings in the US is to almost exclusively avoid soft targets and instead target things...symbols.
Jihadis, on the other hand, go after soft targets almost exclusively. They have a very long track record going back many decades of killing innocents to advance their cause.
So...based on target selection I think that this is very likely a jihadi attack.
Next is the method. Drudge had up a headline this morning that linked to a story where an inside source claims that the bombs were put into 6-liter pressure cookers and then further hidden in duffle bags. Left on the ground. Here is a quote from that story:
These types of pressure cooker explosives have been used in Afghanistan, India, Nepal and Pakistan, according to a July 2010 joint FBI and Homeland Security intelligence report. One of the three devices used in the May 2010 Times Square attempted bombing was a pressure cooker, the intelligence report said.
If there is one thing that jihadis have gotten very skilled with it is the construction of IEDs and these bombs appear to be of that type. So...based on method used I think that this is very likely a jihadi attack.
Regarding the Saudi national in custody: I would not be at all surprised if the guy is innocent. He was supposedly tackled by a civilian running from the scene. Well, just about everyone was running from the scene. Plus, he was injured with shrapnel. Why would the bomber hang out long enough to get injured? If he was a suicide bomber then why wasn't he killed? Clearly, he wasn't a suicide bomber. Okay, so at least he was a Saudi. But this being Boston there are a lot of Saudis in the area and it is not unreasonable or even statistically significant that one might be in attendance at the marathon. He could turn out to be involved but, given the limited and untrustworthy info that has come out so far, for now I will say that he probably wasn't involved.
The professional law enforcement types will have it mostly sorted out within the next 12 to 24 hours. They won't tell us anything until they catch someone but you never know. Until then we have speculation based on known information, reason and common sense.