There are some reports now surfacing that the FBI had Tamerlan Tsarnaev on their radar as recently as November, according to the Telegraph:

As the agency was accused of "dropping the ball" over the case, NBC News reported that Tamerlan Tsarnaev had been seen making six visits to a known Islamic militant in a mosque in the Russian republic of Dagestan.

"If he [Tamerlan Tsarnaev] was on the radar and they let him go, if he was on the Russians' radar, why wasn't a flag put on him, some sort of customs flag?" Mr McCaul asked on CNN, adding that there were clear signs that Tsarnaev had been radicalised during his trip.

The visits came during a six month trip that Tamerlan made to the city of Makhachkala to see his family, NBC said.

According to a local police official, a case file on Tsarnaev was then handed over to the FBI along with a request for further information. However, the FBI never replied.

The agency has already admitted that it interviewed Tamerlan Tsarnaev in 2011 after Russia raised concerns that he was becoming a follower of radical Islam, but found nothing "derogatory" against him and did not pursue the case further.

The 26-year-old, who allegedly orchestrated last Monday's bombings with his younger brother Dzhokhar, was killed in the early hours of Friday morning in a shoot-out with police. It came just hours after police released images of the pair to the public.

In a further twist, Channel 4 News claimed on Sunday that Tamerlan had phoned home in the wake of the bombings and told his mother that the FBI had already called him to accuse him of being responsible.

According to the report, Tamerlan telephoned his mother on Wednesday last week and said he had replied to the FBI's accusations by saying: "That's your problem." The claims emerged from an interview with his father, Ansor.

The FBI declined to comment directly on either claim on Sunday.

However, if either is confirmed, they will add significant weight to the growing chorus of criticism of the FBI, which came on Sunday from senior members of Congress who accused the Bureau of repeatedly "dropping the ball".

Michael McCaul, the chair of House Homeland Security Committee, said the FBI must explain why it failed to keep track of Tsarnaev after the 2011 interview, particularly after he visited his family in Dagestan, which is a known centre of Islamist militancy and training facilities.

Yes, the FBI should have gotten back to the Russians about Tamerlan and discovered what he was doing in Dagestan for 6 months. The Russians were clearly worried about him, but realistically, the FBI had its hands tied. Tamerlan had broken no law, nor even uttered anything that could be construed as seditious or threatening.

At this point, I would blame the Russians more than the FBI. Whatever information they shared with the feds, it wasn't serious enough to have the FBI reopen the Tamerlan file.

I'm not ready to throw the FBI under the bus quite as enthusiastically as some members of congress appear to be doing. Twenty-Twenty hindsight is a wonderful thing and what looks to us like "dropping the ball" may very well turn out to have been proper procedures.

We saw much the same thing during the investigation into 9/11. While there was certainly negligence enough to go around, some critics pointed to straws in the wind as evidence that "warnings" went unheeded. Tamerlan Tsarnaev was an extremely minor blip on the FBI's terror radar. From this point of view, the FBI acted properly and within the scope of the law.

"If only" is not a valid criticism.