To find out whether the Boston Marathon bombing suspects had ties to a terrorism network or anybody else was involved in last month's deadly plot, federal authorities appear to be putting intense pressure on friends of surviving suspect Dzhokhar Tsarnaev and his brother Tamerlan Tsarnaev's widow, Katherine Russell.
Investigators have found explosive residue in the kitchen and bathtub of Tamerlan's home in Cambridge, Mass., according to NPR. This suggests that pressure cooker bombs used in the April 15 attack were at least partly made in the apartment where the slain suspect lived with his 24-year-old wife and child.
Since the bomb exploded during the Boston Marathon, killing three people and injuring more than 260 others, Russell has been living with her parents in North Kingstown, R.I.
While she is assisting investigators, it is learnt that she may not be fully cooperating yet, which has led federal agents to keep an eye on her. They follow her in unmarked vehicles whenever she leaves her parents' house, according to The Associated Press. "It seems to me they don't believe her yet," David Zlotnick, a professor of law at Roger Williams University and former federal prosecutor in the District of Columbia, was quoted as saying.
Authorities say Russell spoke to her husband by telephone after news channels showed his picture as a suspect following the attack. However, Russell's lawyer, Amato DeLuca, has told AP that the last time she saw him was before she went to work on April 18.
Law enforcement officials have met Russell for many hours over the past week, according to DeLuca, who had earlier said his client had no reason to suspect her husband before the bombings.
A key goal of the investigators at this point is "to figure out if she has knowledge of how he became radicalized, who he spoke to, how he may have learned to make the bomb and whether there are others out there who share his views," Ron Sullivan, a professor and director of Harvard's Criminal Justice Institute, was quoted as saying.
Sullivan believes investigators will likely succeed in pressuring Russell to fully cooperate because she is the mother of a young daughter, and would not want to be "deemed as a pariah or ostracized by the whole country."
Authorities have charged three friends of younger brother Dzhokhar, who are from the University of Massachusetts Dartmouth and all 19 years old, for allegedly covering up for the suspect – which could also be a means to force Russell to cooperate, experts believe.
Two of Dzhokhar's friends, identified as Dias Kadyrbayev and Azamat Tazhayakov from Kazakhstan, were arrested for obstruction of justice by removing a backpack with fireworks and a laptop from Dzhokhar's dorm room. The other student, identified as Robel Phillipos, was charged with lying to federal agents about their visit to the dorm room. If convicted, they could get five or more years in federal prison.
The three students have pleaded innocence. Zlotnick says the charging of Dzhokhar's friends suggests authorities could take a similar action on Russell, which forces her to cooperate.
"I think it's to find out ... are there other tentacles here?" seconded Nancy Gertner, a former federal judge in Massachusetts and a professor at Harvard Law School.
Dzhokhar was recently moved from a hospital to a prison medical facility, and faces a potential death sentence if convicted of the terrorism plot.
NPR has reported that Dzhokhar told the FBI that he and his brother initially planned to explode bombs on the 4th of July in Boston, but they changed their plan after they were able to make the bombs well before the target date.