Boston marathon bomb attack 'instigated by brother'

Lawyers for Boston Marathon bombing suspect Dzhokhar Tsarnaev have asked a judge to make prosecutors turn over family-related evidence as they try to build a case that his older brother was the "main instigator" of the deadly attack, the Associated Press reported.

Boston bombing suspect Dzhokhar Tsarnaev Credit: FBI

The defence team is seeking a host of records from prosecutors, including any evidence to support its claim the FBI had asked Tamerlan Tsarnaev to be an informant.

Twin explosions at the April 15 marathon killed three people and injured more than 260 others. Tamerlan, 26, died in a shoot-out with police four days after the attack. Dzhokhar, who was 19 at the time of the bombings, was captured soon after his brother's death and pleaded not guilty to 30 charges.

Dzhokhar's lawyers wrote: "Any surveillance, evidence, or interviews showing that Tamerlan's pursuit of jihad pre-dated Dzhokhar's would tend to support the theory that Tamerlan was the main instigator of the tragic events that followed."