I've been going through materials related to the FBI's investigation of Tamerlan Tsarnaev and killing of Ibragim Todashev, and I came across an interesting snippet from a June 13, 2013 House Judiciary Committee hearing on FBI oversight. Former FBI Director Robert Mueller told Congress that the FBI became aware of Ibgraim Todashev through the phone dragnet, and possibly also through the FAA Section 702 content collection authority (on which PRISM depends). (We still don't know exactly when the FBI became aware of Todashev. That'd be useful to know.)
We know that prior to his death in May 2013, the FBI was dedicating significant resources to monitoring Todashev in Florida. The operation included aerial monitoring, using either a drone or a single-engine Cessna, and a large in-person surveillance team.
Here's the relevant portion from the June 2013 hearing.
Mr. COHEN: There was another fellow that was a friend of Tamerlan’s who was in Florida and being investigated by FBI agents and they killed him. You remember that, don’t you?
Mr. MUELLER: I would say that there was a response to a threat that resulted in——
Mr. COHEN: What was the threat? Because at first the reports were there was a knife or something, and then later they said there was no weapon.
Mr. MUELLER: That’s still under investigation.
Mr. COHEN: How did you get knowledge of Todashev and his involvement in this crime? Was it through the FSB or was it your own investigation?
Mr. MUELLER: Actually, it was a number of ways, including one of the programs that is under scrutiny today.
Mr. COHEN: What do you mean, 215 and 702?
Mr. GOODLATTE: The time of the gentleman has expired. The Director can answer that question.
Mr. COHEN: Yeah, is it 215 and 702, is that what you mean?
Mr. MUELLER: There was effort done in terms of that particular program as well, but I will tell you that we came upon him in a variety of ways.
Before anyone takes this to mean that the 215 and 702 programs "worked" or provided any value to investigators, remember that the FBI would have had zero trouble getting Tsarnaev's phone records with a mere subpoena. The same goes for the deceased suspect's internet and email metadata. Once they discovered these records, agents would also have had no problem obtaining information about anyone Tsarnaev was in contact with, either via email or by phone.
On a related note, when authorities leaked to reporters that they had "hard evidence" linking Todashev and Tsarnaev to a gruesome triple murder in Waltham, Massachusetts, they claimed one of those pieces of hard evidence was phone location records. ABC news reported:
The officials also said records of cell phones used by the Tsarnaevs appears to put them in the area of the [Waltham] murders on that date.
Of course, we don't know if this is true. But according to James Clapper, the NSA was actually running a domestic cell phone tracking pilot during 2010 and 2011, at the time the murders took place. So it's possible that in April 2013 they actually had that old data, and after the Boston marathon bombings looked at Tsarnaev's location information during those years, in addition to whatever information his cell carrier held on him when he died.
But this revelation also raises a troubling question: Why didn't law enforcement subpoena or obtain a court order to demand cell phone location records for the area around where the murders took place back when the case was fresh, in September 2011? Certainly the Middlesex District Attorney's office was well aware of how to use cell tower dumps in homicide investigations. That's not mere speculation. In April 2010, Joseph Gentile, a prosecutor from that office, actually taught a continuing legal education session on the very subject:
The one-year mark of the Boston marathon attacks is approaching shortly, and journalists are likely going to spend a lot of time covering both the Waltham murders and the events of April 2013. Perhaps someone should ask the Middlesex District Attorney if cell phone location records were obtained during the course of the 2011 murder investigation, and if not, why not. Those records seem like an odd thing to only stumble upon more than two years after the crime took place.