Closing arguments contrasted the prosecution's partnership theory with the defense's acknowledgment of participation and emphasis on Tamerlan's leadership. Judge O'Toole instructed jurors on all 30 counts and the burden of proof, denied a defense mistrial motion, and designated six alternates. The remaining 12 jurors would begin deliberations the next morning.
Full day summary
Judge O'Toole individually questioned 18 jurors about media exposure and outside discussions. Jurors reported compliance with the court's restrictions. He then instructed them on all 30 counts, explaining aiding and abetting, conspiracy, coconspirator liability, and required unanimous findings. He distinguished affirmative assistance from mere presence or knowledge and explained advance knowledge for firearm aiding and abetting.
In closing, Aloke Chakravarty argued that the defendant and Tamerlan acted as partners in a coordinated terrorist campaign. He cited recordings, communications, physical evidence, extremist materials, and the boat writings, and sought guilty verdicts on every count. He acknowledged that the evidence did not identify who shot Officer Sean Collier while arguing that both brothers were responsible. Judy Clarke acknowledged the defendant's participation in the bombing, carjacking, theft, and Watertown confrontation but argued that Tamerlan planned and led the crimes. She attributed bomb preparation and Collier's shooting to Tamerlan, disputed the prosecution's account of independent radicalization, and argued that the evidence did not establish how or by whom the second bomb was detonated.
William Weinreb's rebuttal challenged the defense's account and argued for partnership and independent action. He again acknowledged uncertainty about Collier's shooter and also acknowledged uncertainty about the extremist materials' original source. These were counsel's arguments, not new testimony or court findings.
The judge completed instructions on evidence, credibility, reasonable doubt, unanimity, and the defendant's right not to testify. At sidebar, he denied the defense's mistrial motion concerning the closing montage, alleged comments on the defendant's silence, and a disputed fireworks reference. He declined to change challenged instructions; counsel preserved objections and discussed indictment redactions. Six jurors were designated as alternates, leaving 12 to deliberate. Deliberations were deferred until the following morning at nine o'clock.