Day 40 - March 26, 2015

FBI chemist David McCollam testified that residues from both Boylston Street scenes were consistent with burned pyrotechnic material and that Watertown bulk powder was pyrotechnic flash-powder-type material. He reported pyrotechnic residues in Norfolk Street filters and on Honda CR-V gloves, plus physical black powder grains in four Norfolk Street samples. His testing identified substances but did not measure their quantities or identify a specific assembly location. The court excluded an undisclosed expert opinion comparing residue amounts with the explosives involved. On cross-examination, McCollam distinguished the findings on individual gloves and said filters recorded as coming from a UMass Dartmouth dorm room screened negative for the typical explosive-residue traces tested by the laboratory. His knowledge of collection locations came from information supplied with the samples. On redirect, he discussed intact fireworks attributed to the dorm room through laboratory submissions and intact pyrotechnic mixture in a landfill bag. An objection prevented an answer about a single device-production location. FBI hazardous-device examiner Edward S. Knapp described the Boylston Street pressure-cooker bombs and Watertown devices. He compared recovered fragmentation with an Inspire article and demonstrated reconstructed remote-control systems. Scene B's Spektrum receiver was incompatible with the recovered Flysky transmitter; the original Scene B transmitter had not been found. Separate exemplar transmitters activated the mockups independently, but Scene B's original transmitter configuration and exact operating ranges remained unknown. The court allowed exhibition of the mockups while reserving admission. During cross-examination, it excluded proposed transmitter-range evidence under Rule 403 at sidebar. Knapp also discussed purchase records, including an R/C car receipt bearing Tamerlan Tsarnaev's name. Jennifer Hammers testified that Krystle Marie Campbell died from blast injuries, with damaged blood vessels causing fatal blood loss. Over a defense objection concerning disclosure and foundation, the court allowed her estimate that Campbell could have survived from seconds to approximately a minute. Autopsy photographs were shown to the jury, not on public monitors. The defense asked no questions, and the court adjourned until Monday.