William G. Gross

William G. Gross testified for the prosecution on Day 29 about Marathon security and the police response to the explosions. Under questioning by Aloke Chakravarty, he described his assignment as Zone 6 commander on April 15, 2013, covering Audubon Circle through Kenmore Square, along with interagency planning, suspicious-package precautions, and explosive-detection sweeps.

Gross said congested radio communications prompted him to call the police operations center, where personnel reported two explosions whose type was not yet known. He sent additional officers to Boylston Street and later stopped the race at Audubon Circle. He described responders, civilians, and businesses helping injured people reach safety within approximately 21 to 22 minutes, including transport in police vehicles when ambulances ran out. His account also covered further explosive-detection sweeps, a secured crime-scene perimeter, and transportation restrictions amid uncertainty about additional threats.

Gross attributed the assessment that the explosions were bombs to the Unified Command Center. He described the FBI assuming investigative jurisdiction that evening, while qualifying the timing, and said he believed the public had supplied more than 4,000 hours of video, along with pictures. No specific exhibit was offered or admitted during his testimony. David Bruck declined questioning for the defense, and the court excused Gross.