How to detect tape tampering

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As the number of requests for forensic tape examinations increases to include new digital formats, it has become apparent that attorneys appreciate proper forensic testing techniques to insure Daubert and Rule 26 requirements are met.

When an audiotape becomes suspected of tampering, it may be forwarded to a qualified forensic examiner for authentication. Poten-tial problems are credibility questions relating to the tape recorder operator, chain of custody contradictions and differences between the content of the tape and testimony.

FBI Guidelines Set the Standard

Due to the nature of the allegations surrounding tampering issues, the examiner requires specific items and information.

The Federal Bureau of Investigations, for example, has a list of required data and materials, including the original tape, and the tape recorders and related components used to produce the recording. FBI protocol also calls for any written records of any damage or maintenance done to the recorders, accessories and other submitted equipment, as well as a detailed statement from the person(s) who made the recording describing exactly how it was produced and the conditions that existed at the time.

As for those conditions, the FBI guidelines consider the power source, such as portable generator or dry-cell batteries, and the input, such as telephone, radio frequency transmitter/receiver, miniature microphone, etc.

Environment is also a factor, such as telephone transmission line, street traffic, etc., and other background data, including the number of individuals involved in the conversations, enhancement issues, etc., and foreground information, such as number of individuals involved in the conversation, general topics of discussion, closeness to microphone, transcript verification, etc.

Finally, also to be considered, if applicable, are the magnetic tape, such as brand, format, when purchased, whether previously used, and the recorder operation, such as number of times turned on and off in the record mode, type of keyboard or remote operations for all known events, uses of voice-active features, etc.

The Expert’s Role

A forensic expert is trained to correlate his observations of such anomalies with machine functions to interpret events in the following ways.

Critical listening, or the use of human analytical capabilities to locate anomalies. The forensic scientist listens with proper headphones to the original tape using high-quality analytical equipment.

He performs a preliminary overview of the original tape and notes events including starts, stops, speed fluctuations, and other variations requiring further investigation. He then examines record events and categorizes them as environmental or non-environmental. After examining recorded events, the expert analyzes background sounds, listening for abnormal changes in environmental sound.

Physical Inspection, or the inspection for tampering via a thorough visual examination of the tape itself. The expert inspects the housing for pry marks, welding breaks, or size, label and date that are inconsistent with the alleged recording date. He also measures the tape and assures the splicing of the magnetic tape to the leader is consistent with normal manufacturing process. Any other splices are noted as possible alteration.

Magnetic Development, or the direct visual observation of the magnetically “developed” tape. This is done to find track widths, the type of recorder used, and the presence or absence of residual speech signals.

Spectrum Analysis, or the use of specialized computer equipment and programs to produce visual interpretation of frequency-versus-time displays. This allows the expert to view the entire spectrum, or to zoom in on an area of particular interest, thereby helping to characterize the acoustic quality of anomalies and identify their source.

Waveform Analysis, or the use of a computer-generated display representing time-versus-amplitude of recorded sounds in graphic form. With such analysis, the expert can sometimes measure signal return time that reveals how long a recorder had been turned off.

He can identify record-mode events, including the measurement of record-to-erase-head distances, determination of the spacing between gaps in multiple-gap erase heads, and inspection of the signature shape and spacing of various record event signals.

Finally, Recorder Performance, or the execution of various electrical and mechanical measurements of standard and modified recorders for use in finding possible origins of buzz sounds, hum, etc.

Conclusion

The prevalence of technology in our daily lives has increased in recent years, and that technology is changing rapidly. In the legal world, this means that more and more cases with technology are presenting themselves, including cases involving video and audiotape.

Yet, each case comes with its own subtle differences, and as such, the expert must work closely with the attorney to find the best method of presenting the expert’s analysis, results and conclusions so they are clear to the court, jurors, parties and the public.

Steve Cain is a board-certified and court-qualified expert in video and audiotape analysis, and he is the president of Forensic Tape Analysis, Inc. in Burlington. He can be reached at info@tapeexpert. com.