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Will a trunk-mounted radio damage computer evidence?

Special thanks to Sgt Fred Deltorchio and the Benicia (CA) Police Department for their assistance with this test.

Recently we have seen several alarming warnings about the dangers of placing computer evidence in the trunk of a police car containing a trunk-mounted radio. These articles claimed that the RF energy of the nearby radio would corrupt the computer evidence. We found these claims interesting, so we decided to conduct a test. The results showed absolutely zero corruption of magnetic media. While this test only used one type of trunk-mounted police radio, the results may be similar for other types of modern radios. We would be interested to hear from anyone who believes they have had computer evidence corrupted by a trunk-mounted radio. In the future we plan to conduct similar tests with other brands of radios operating in other frequency ranges.

The tested media was four 3.5" 1.44MB floppy disks and one Quantum ProDrive 80MB SCSI hard drive. Using a version of a disk duplication program that is exclusively for law enforcement use, we created four identical floppy disks. We then ran a program that for each disk generated a CRC value for each file on the disk. We placed two disks each in paper envelopes. The hard disk was formatted and approximately 36 megabytes of data was written to it. We then ran the same CRC generating program for the hard disk. The hard disk was placed in an anti-static bag and packed in paper in a cardboard box.

One envelope containing the 3.5" disks was placed directly between the transmitter/receiver and the mounting bracket of a GE MVS VHF trunk-mounted police radio (mounted on the side wall of the trunk). This radio operates in the 150MHz band. The second envelope was placed on the floor of the trunk opposite the radio. The box containing the hard disk was placed in the center of the trunk. The police car also had a trunk-mounted cellular phone transmitter/receiver mounted next to the VHF radio.

All disks remained in the trunk for 3 days. The police car was used almost continuously during that time. After 3 days the disks were removed and an analysis conducted to see if any information had been changed or corrupted.

Conclusion: The contents of all four floppy disks and the hard disk were unchanged in any way. The CRC values of all files were checked both before and after the test period. Even the disks that were placed directly against the transmitter/receiver were not affected. We do invite others to conduct their own carefully monitored tests and would be interested in compiling the results with different brands and frequency trunk-mounted radios. While this test does not alleviate the necessity to properly safeguard the integrity of computer evidence, it does appear that magnetic media is less corruptible than some believe.

Download the full test results, which include the raw data. This document is a zipped Word for Windows version 2.0 file (RTF 25k), which is viewable in both Windows and Macintosh versions.

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