Expert witnessFlorida Bureau of Fire, Arson and Explosives Investigation

Brock Dietz

Forensic video analyst who testified for the State in the 2019 Garcia–Magbanua trial and the 2022 Magbanua retrial about Premier Gym and city-bus footage, with the 2022 record additionally covering ATM still images.

AppearedGarcia–Magbanua Magbanua Retrial

92 lines·5 proceedings·2 trials

About

Brock Dietz was a law-enforcement witness with forensic-video training who prepared and explained surveillance, ATM, and city-bus imagery used by the State. His work included re-digitizing source files, isolating requested time periods, creating highlighted or shortened clips, producing ATM stills, and drawing attention to vehicles or people in the imagery. He testified that the clarified clips retained their original timestamps and that he did not change luminance or add or remove people or vehicles. When questioned about the preparation process in the 2019 joint trial, he acknowledged that the State Attorney's Office selected material for clarification and requested revisions, and that he did not prepare a side-by-side comparison; he explained that the visual aids were made on a working copy while the original footage remained unchanged. At Magbanua's retrial, the underlying data and prepared surveillance, ATM, and bus exhibits were admitted without defense objection, and the defense waived cross-examination.

Trial Record (5)

GMGarcia–MagbanuaSep 26, 2019 – Oct 11, 2019Called by prosecution

Testifying on Day 1, Brock Dietz described preparing clarified surveillance and bus-video clips while leaving the original footage unchanged. Cross-examination addressed the State Attorney's Office-directed revisions to Government's Exhibits 124 and 125.

Day 1

Sep 26, 2019

DirectBrock Dietz - DirectBrock DietzGeorgia Cappleman2highlights32lines spoken

Summary

Brock Dietz described how he prepared annotated Premier Fitness and city-bus surveillance clips without changing their underlying subjects or brightness.

Highlights (2)

testimony highlightDietz described his forensic video-analysis experience and the ways he can clarify, enlarge, slow, and highlight existing video images for a jury.Open in transcript →Watch this moment ▶

Quote“The technique that I use is basically clarifying video. The way I like to describe it is simply the video's been recorded, and I clarify it so that the judge and jury can make an educated decision on what they're seeing.”— Brock DietzDietz characterized his work as clarification of recorded material rather than creation of new visual information.Open in transcript →Watch this moment ▶

CrossBrock Dietz - CrossBrock DietzSaam Zangeneh2highlights31lines spoken

Summary

Dietz said the State directed five rounds of clarifications to the surveillance-video exhibits, with a final copy provided the week before trial.

Highlights (2)

evidence eventDietz said the final copy of the video exhibits was provided the previous week and that later edits added requested clarifications, including removing part of the victim's time in a car.Open in transcript →Watch this moment ▶

Quote“Five times.”— Brock DietzDietz gave the number of times he had gone through the original footage while answering the defense's question about alterations.Open in transcript →Watch this moment ▶

RedirectBrock Dietz - RedirectBrock DietzGeorgia Cappleman2highlights6lines spoken

Summary

Dietz said the surveillance-video clarifications were made on a working copy and did not alter the original footage.

Highlights (2)

testimony highlightDietz testified that the original video was never altered; his clarifications were made to a working copy provided to the State.Open in transcript →Watch this moment ▶

Quote“At no point, at no point was the original ever worked on. I always work on a working copy.”— Brock DietzDietz directly addressed whether the original surveillance footage had been altered.Open in transcript →Watch this moment ▶

KMMagbanua RetrialMay 18, 2022 – May 27, 2022Called by prosecution

On Day 1, Brock Dietz provided forensic-video foundation testimony for surveillance clips, ATM stills, and StarMetro bus-data materials offered by the State.

Day 1

May 18, 2022

DirectBrock Dietz - DirectBrock DietzGeorgia Cappleman5highlights22lines spoken

Summary

Forensic video analyst Brock Dietz described preparing surveillance clips and stills; the court admitted the related Premier Gym, ATM, and bus exhibits.

Highlights (5)

Quote“I have been performing forensic video analysis since 2002. For the past 20 years, I've analyzed over 830 different video and audio submissions.”— Brock DietzDietz described the experience underlying his forensic-video work.Open in transcript →Watch this moment ▶

evidence eventThe court admitted the stipulated Premier Gym raw data as State's Exhibit 117 and Dietz's prepared video clips as State's Exhibit 89.Open in transcript →Watch this moment ▶

evidence eventAfter Dietz identified the ATM stills as fair and accurate images from the raw data, the court admitted State's Exhibits 37 through 43.Open in transcript →Watch this moment ▶

Quote“Correct. I was able to isolate the victim's vehicle as well as the suspect vehicle.”— Brock DietzDietz summarized his work on the bus-surveillance data.Open in transcript →Watch this moment ▶

Show all 5 highlights

evidence eventThe court admitted the raw bus surveillance data, Dietz's bus clips, and one identified bus-data image as State's Exhibits 118, 90, and 4.Open in transcript →Watch this moment ▶

Cross WaivedBrock Dietz - Cross (Waived)Brock DietzChristopher DeCoste1highlight

Summary

Defense waived cross-examination of Brock Dietz, who was excused.

Highlights (1)

procedural actionDefense waived cross-examination, and the court excused Brock Dietz before the State called its next witness.Open in transcript →Watch this moment ▶