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The Boston Marathon bombings is an unusually complex case, involving two main suspects and their relatives on two continents and hundred of investigators.

Investigators continue to focus on the main suspects, Tamerlan Tsarnaev, 26, who died after a police shootout, and his younger brother, Dzhokhar Tsarnaev, 19, who is now recovering from bullet wounds.

Meanwhile, the number of people involved in the case as suspects, lawyers and experts continues to grow. Here are the individuals playing an important role:

Judy Clarke, defence lawyer

Ms Clarke, a 60-year-old lawyer based in San Diego, is defending Tsarnaev. A "master strategist" in death penalty cases, , she has represented some of the most difficult clients in recent US history.

"She has stood up to the plate in the kinds of cases that bring the greatest disdain from the public," as Gerald Goldstein, a Texas lawyer who knows her well, told the newspaper.

She represented Ted Kaczynski, known as the Unabomber, and al-Qaeda operative Zacarias Moussaoui. Another one of her clients, Jared Lee Loughner, shot and killed six people and wounded Congresswoman Gabrielle Giffords.

Richard DesLauriers, FBI special agent in charge

Mr DesLauriers, 53, has for years been involved in high-profile cases. He announced the arrest of Boston crime boss James Bulger in June 2011, for example.

He is known as "meticulous" and "a perfectionist" in his approach to investigations, a former law enforcement officer who has been involved in federal cases told the ����ý.

"Rick is the real deal," David Kris, former US assistant attorney general for national security, .

Katherine Russell, widow of Tamerlan Tsarnaev

A native of Rhode Island, Ms Russell, 24, met her future husband while a student at Suffolk University. Her father is a physician and her mother a nurse.

Ms Russell married Tsarnaev in 2010 and afterwards converted to Islam. They have a three-year-old daughter. They liked to take walks on Norfolk Street in Cambridge, where they lived. "She wore her ethnic scarf," a neighbour, Lila Lyman, told the ����ý.

Her attorney, Amato DeLuca, has said she does not speak Russian and had nothing to do with the bombings.

Dias Kadyrbayev, former student

The 19-year-old Kazakh was arrested on 20 April on suspicion of immigration violations. He was later charged with destroying evidence in the bombings case.

He is a former student at the University of Massachusetts at Dartmouth, where Tsarnaev had been enrolled. He reportedly drove a car with a license plate that read "Terrorista #1".

Azamat Tazhayakov, student

A University of Massachusetts at Dartmouth student who is also originally from Kazakhstan, Tazhayakov, 19, was a roommate of Mr Kadyrbayev.

He was in the US on a student visa and has also been charged with destroying evidence in the bombing case.

Robel Phillipos, former student

A former University of Massachusetts at Dartmouth student, Mr Phillipos, 19, of Cambridge, Massachusetts, went to high school with Dzhokhar Tsarnaev.

They were both students at Cambridge Rindge and Latin High School. Mr Phillipos was recently charged with lying to impede the investigation.