Edward S. Knapp

Edward S. Knapp testified for the prosecution on Day 40 about his FBI laboratory examination and reconstruction of the Boylston Street and Watertown explosive devices. He described examining more than 1,300 evidence submissions and using purchased exemplars, component comparisons, manuals, and functionality testing to interpret fragmented remains. He identified the Boylston Street bombs as pressure cookers carried in backpacks, with low explosive and hobby-car remote-control components. Both contained BBs; Scene B also contained small nails.

Knapp distinguished Scene A's Flysky system and toggle switch from Scene B's Spektrum receiver and Duratrax controller. He testified that the Scene B receiver was incompatible with the recovered Flysky transmitter and that no Spektrum transmitter had been found. Using separate exemplar systems, he demonstrated that each transmitter activated its own mockup light, not the other. He acknowledged that the missing Scene B transmitter's configuration and the devices' exact operating ranges were unknown.

His comparisons also covered a smaller Watertown pressure cooker, intact and exploded pipe devices, and a plastic-container device. He explained that the pipe mockups represented recovered intact devices rendered safe, rather than the exact appearance of the exploded pipes. He compared descriptions in Inspire with recovered fusing and fragmentation materials. The court reserved admission of the mockups and, after Watkins challenged the foundation for transmitter-binding testimony, allowed Knapp to explain binding his exemplar without offering an opinion that the recovered transmitter and Scene A receiver were bound.

On cross-examination, Watkins tested uncertain cardboard placement, the Scene A arming requirements, evidence routing among laboratory disciplines, and Knapp's recollection. Knapp confirmed that the Scene A system needed battery charge and an armed toggle switch before awaiting transmitter input. After consulting his report, he identified the Q199 cardboard fragments as coming from Scene A. The court admitted their photograph as Defense Exhibit No. 3093 but barred questions about fingerprint results and related expertise.

Knapp identified a February 8, 2013, R/C car receipt bearing Tamerlan Tsarnaev's name and said he believed an April 8 purchase record concerned Spektrum products associated with Scene B. He limited his account of Inspire to the portion he had read, which did not mention radio-controlled cars as a fusing system. Watkins sought transmitter-range evidence concerning the defendant's knowledge and sophistication; prosecutors disputed its foundation and argued it could misleadingly suggest that Tamerlan detonated the second bomb. The court excluded that evidence under Rule 403.