The death of one suspected bomber and the capture of the other on Friday in the Boston Marathon bombing may not be the end of arrests in the case.  Yesterday afternoon, FBI and DHS agents arrived at the same New Bedford apartment complex where they had detained three people in the Friday manhunt for Dzhokhar Tsarnaev, this time taking two away in handcuffs:

Agents wearing FBI and Department of Homeland Security jackets detained two men at the Hidden Brook apartment complex just hours after releasing three people believed to be associated with Boston Marathon bombing suspect Dzhokhar Tsarnaev.

A neighbor who declined to identify herself said the same two men were among the three people taken into custody by the FBI Friday afternoon.

An FBI spokeswoman could not provide any information on the two men, both of whom were led away in handcuffs around 3:50 p.m. Saturday, or anything related to the apartment, citing the “ongoing” nature of the investigation.

Interestingly, this time the FBI and DHS didn’t come alone.  A consular vehicle from an unidentified  nation also arrived, and transported two women out of the complex after the arrests took place:

Earlier Saturday afternoon, a silver mini-van with consulate license plates arrived at the Carriage Drive apartment along with the FBI and Homeland Security, and stayed a half an hour longer than the agents.

The van left with two women, neither of whom appeared to be restrained. One was carrying a pink backpack as she exited the apartment and ran into the van, which sped away as the women told reporters they did not wish to comment.

We noted the brief detention of two men and a woman on Friday afternoon, but the FBI left after Dzhokhar Tsarnaev was apprehended in Watertown.  The police told the Standard-Times on Friday that the two men were believed to be fellow students at the University of Massachusetts at Dartmouth.

Meanwhile, the Daily Mirror in the UK reports that the FBI is investigating the possibility that the Tsarnaev brothers were part of a “sleeper cell” in the US that could contain a dozen operatives:

The FBI was last night hunting a 12-strong terrorist “sleeper cell” linked to the Boston marathon bomb brothers.

Police believe Tamerlan and Dzhokhar Tsarnaev were specially trained to carry out the devastating attack.

More than 1,000 FBI operatives were last night working to track down the cell and arrested a man and two women 60 miles from Boston in the hours before Dzhokhar’s dramatic capture after a bloody shootout on Friday.

A source close to the investigation said: “We have no doubt the brothers were not acting alone. The devices used to detonate the two bombs were highly sophisticated and not the kind of thing people learn from Google.

“They were too advanced. Someone gave the brothers the skills and it is now our job to find out just who they were. Agents think the sleeper cell has up to a dozen members and has been waiting several years for their day to come.”

It’s important to keep in mind that the FBI will be investigating all sorts of possibilities in connection to the attack.  The travel pattern of Tamerlan Tsarnaev provides the potential for significant contact with radicals in Dagestan and Chechnya, but those contacts have yet to be established.  Until the FBI and intelligence agencies find those contacts and develop those leads, they will keep all potential theories in play.

Speaking of which, House Intelligence chair Mike Rogers told NBC’s Meet the Press that Tamerlan may have traveled to Russia using an alias:

Chairman of the House Intelligence Committee Rep. Mike Rogers, R-Mich., said on NBC’s Meet the Press Sunday that when Tamerlan Tsarnaev, the Boston Marathon bombing suspect killed Friday in a shootout with police, travelled to Russia in 2012, he may have done so under an alias.

Tamerlan Tsarnaev’s six-month stay in Russia last year “becomes extremely important” as a key to the investigation of the Boston bombings, Rogers told NBC’s David Gregory. His visit to Russia “would lead one to believe that that’s probably where he got that final radicalization to push him to commit acts of violence and where he may have received training” in terrorist techniques. Rogers, a former FBI agent, said the FBI had questioned Tamerlan Tsarnaev after being given information from a foreign intelligence service “that they were concerned about his possible radicalization.” …

But appearing on CNN’s State of the Union Sunday, Sen. Lindsey Graham, R- S.C., said Tamerlan Tsarnaev is the kind of person “you don’t want to let out of your sight,” and that it was a mistake for federal authorities to have lost track of him.

“Either our laws are insufficient or the FBI failed, but we’re at war with radical Islamists and we need to up our game,” the South Carolina Republican told CNN.

How did we find out so quickly about Tamerlan’s travels, though, if he traveled under an alias?  Or did the FBI keep closer track of Tsarnaev than Lindsey Graham thinks?

Although Dzhokhar Tsarnaev remains in serious condition, officials plan to charge him in federal court quickly, perhaps as soon as today:

Federal officials hope to bring charges against Dzokhar Tsarnaev as early as today, a Department of Justice official tells CNN’s Pamela Brown.

A law enforcement official tells CNN that Tsarnaev might be arraigned at the hospital. The 19-year-old suspect in the Boston Marathon bombing remains in serious, stable condition, under heavy guard at a Boston hospital. A judge is coming to his bedside.

Once charged in civil criminal court, options for investigators begin to narrow considerably in regard to interrogation.  It’s possible that they have already found what they wanted from the surviving Tsarnaev brother, which may be why FBI, DHS, and a consular van reappeared at the New Bedford apartment complex.

Update: The agents arrived yesterday afternoon, not last night.  I’ve corrected that in the first paragraph.

Update: The New York Daily News has photos of the two men, and report that they have been detained on “immigration violations”:

Two foreign nationals — who are believed to be associates of the alleged Boston Marathon bombers — were arrested Saturday on immigration violations, authorities said.

The men, identified by neighbors as 19-year-olds from Kazakhstan, drove around in a black BMW with the mock license plate, “TERRORISTA #1.”

The pair was hauled out of their New Bedford apartment in handcuffs about 3:50 p.m. The raid was carried out by Immigration and Customs Enforcement agents, a spokesman told the Daily News.

Immigration violations from Kazakhstan? Those don’t usually require a consular van to collect associates. This is still a fluid situation and this lead may end up being nothing at all, so keep an open mind. The fact that federal investigators returned the next day and diplomatic intervention was required indicates that this is something a little more serious than a visa violation, or at least is suspected of being so.

Update: Bear in mind that this could still be (relatively) unrelated to the bombing.  The FBI may have identified Tsarnaev’s associates and detained them on Friday to get more intel on their fugitive, and then discovered an immigration issue either during or shortly after their interrogation.  Given the nature of the larger case, they may have alerted the consulate to get involved immediately and accelerated the processing of the immigration issue to get them out of the way.  That’s at least a possibility, so again, keep an open mind.

Update: Looks like KDKA has heard what the Mirror reported earlier:

New at 1:00 FBI Source: suspects could have ties to 12-member terrorist sleeper cell group. @tunein http://t.co/mbfMTnNh2q

— 100.1 FM and AM 1020 KDKA (@KDKARadio) April 21, 2013

Stay, er, tuned.

Update: Dzhokhar isn’t saying much, at least not verbally:

RT @thegarance: CBS: “neck wound is the primary reason why Tsarnaev is unable to speak with investigators” http://t.co/E0KJyeGymh

— Gabriel Malor (@gabrielmalor) April 21, 2013

Mayor Thomas Menino wondered aloud earlier today whether he’d ever be able to talk with investigators.  Let’s hope that doctors make that happen as soon as possible.