Saudi Arabia warned US about bomber in writing, by name.

[Mr. Morden]

So did Tamarlan actually get some training on the bombs when he was in Russia or not?  And if so, who did he get it from?  Seems like he had to have had some contact with *someone* besides his brother over all of this.  Otherwise, how did he ever get on the radar of either the Russians or the Saudis in the first place?

[Mr. Morden]

The story is being denied now, but still, how would Saudi Arabia even know anything about Tsarnaev to begin with??

I don't know.  How did Russia know there was something suspicious about him, such that they warned the FBI?  Are they spying on the internet viewing habits of every single expatriot of the Caucasus?  That's the part that I still don't get.

[Mr. Morden]

The story is being denied now, but still, how would Saudi Arabia even know anything about Tsarnaev to begin with??

I don't know.  How did Russia know there was something suspicious about him, such that they warned the FBI?  Are they spying on the internet viewing habits of every single expatriot of the Caucasus?  That's the part that I still don't get.

Because they lived in Russia, and travelled to Russia, and the parents moved back to Russia.

So the Russian security services read the email of everyone who emigrates from that region or what?  What did he do to get on their radar, such that they realized there was a problem, enough to warn the FBI about him?

[Mr. Morden]

Ah, OK.  Looks like I can answer my own question.  Looks like Tamarlan was talking to a Canadian man "who had joined the Islamic insurgency in the region", which led them to start spying on him:

http://www.usatoday.com/story/news/world/2013/04/30/russia-tsarnaev-surveillance/2125095/

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The story goes on to say that Tamarlan was attending a mosque Dagestan that was known for attracting radicals.  They might have had the mosque under surveillance as well.