Rooftop Unit Case: Destroyed Original, Expired Certificate, and an Unlogged Edit
A code enforcement officer responds to a night complaint about a rooftop mechanical unit. Using a handheld Class 1 meter with a removable SD card, he records a 30-minute file, photographs the meter display, and notes the address and time on a paper form. At the office he copies the file to the case folder, renames it 'case123_final.wav', converts it to MP3 for the shared drive, and deletes the original from the SD card to free space. The instrument's calibration certificate expired two months earlier, although the field check with the calibrator was within 0.2 dB. On the paper form the distance from the unit is written as 12 m; while typing the report he re-measures on a map, decides 15 m is correct, and types 15 m without noting the change. Defense counsel requests 'all raw data and the original recordings.' The supervisor asks whether the file can still be used.
1. Identify the documentation and evidence failures and their consequences.
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- Destruction of the original recording. Deleting the SD card file is spoliation; it can lead to exclusion of the evidence or an adverse inference, and it cannot be cured after the fact.
- Lossy conversion. The MP3 changes the signal and may strip metadata, so the shared-drive file is not the measurement; the renamed WAV is an unauthenticated copy with no recorded mapping to the original.
- No hash at acquisition or transfer, and no transfer log, so the file's integrity cannot be demonstrated.
- Expired calibration certificate. The 0.2 dB field check only compares meter to calibrator; if the calibrator's own laboratory calibration has lapsed, traceability to national standards is broken and the instrument's conformance to IEC 61672-1 can be challenged.
- Unannotated 12 m to 15 m change. The paper form and the report now conflict with no explanation; the contemporaneous record has effectively been overwritten.
- Photographs of the display without documented time, place and operator add little independent value.
2. Set out a corrective evidence-handling protocol for this program.
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At download, compute a SHA-256 hash of each raw file and record it with instrument serial number, file name, date/time, operator and location. Write the original once to the evidence repository, mark it read-only, and work only from copies; image or retain the SD card and never delete files from it for space. Maintain a signed transfer log at every handoff. Keep instrument and calibrator certificates current and filed with the case; a lapsed certificate is a scheduling failure, not an acceptable condition.
Correct paper records with a single strike-through, initial and date - never erasure. For any change to a typed report, issue a dated, signed errata memo stating the original value, the corrected value, the basis (here, a map re-measurement) and who authorized it, and cross-reference the original document. A short standard operating procedure plus periodic audit would have prevented every one of these failures.
3. How should the officer testify about the destroyed original and the changed distance?
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Authenticate what can be authenticated and concede what cannot. Testify to training, the instrument and its field check, the measurement point, and what was observed. Then state plainly that the original file was deleted under a retention practice that has since been corrected, that no hash was taken, and that the MP3 is a derivative - do not claim it is the original. Expect the loss to reduce or eliminate the weight of the measurement.
On the distance, explain the sequence from the record: the paper form was the contemporaneous note, the report value came from a map re-measurement, and the errata memo documents the change. If it cannot now be established which value is correct, say so; a witness who guesses under cross-examination loses the rest of the testimony. Disclose the errata memo and the transfer log to opposing counsel in full and in advance. The candid account preserves credibility for the observations that remain reliable.