As this ScienCentral News video reports, a new high-tech tool for possibly recovering such evidence is right in the home computer.

Seeing is believing

This technology was originally developed by physicists at the University of California, San Diego in 1996 as a tool for the hard-disk industry. When government researchers were asked by the FBI and the National Transportation Safety Board for a way to recover information from audio tape, they adapted the scanning magnetoresistive microscope for forensic use. Researchers at the National Institute of Standards and Technology (NIST) and the National Telecommunications and Information Administration’s Institute for Telecommunication Sciences came up with this special kind of microscope.

The instrument works by painstakingly passing a piece of magnetic material, such as tape, under a tiny sensor from a computer hard drive. As the sensor moves around on top of the magnetic pattern embedded in the material, it maps the magnetic field. This information can then be reconstructed in a computer to get an image, or interpret the data directly into sound.

According to NIST scientist David Pappas, the main advantage of the technique is that it gives the actual size and strength of the magnetic field. (The current technique, which uses magnetic fluids, gives no indication of how strong the field is and can also ruin digital tapes and disks.) "In this technique we can actually go in and see how strong and what the direction is, and when we do that we can actually decode information that’s on a tape," says Pappas.

Sound advice

But it may not be just what’s on the tape that can now be deciphered. The FBI is testing the technique for analyzing evidence such as erase marks. One of the most famous erasures of all time—the 18 1/2-minute gap from the Watergate tapesmay now come under scrutiny. Officials at the National Archives and Records Administration are considering using the device to examine the gap and hopefully fill it in.

But Pappas isn’t overly optimistic. "If a cassette recorder completely erases a signal we cannot recover that signal," he says. "It’ll be comparable to if you wrote something on a piece of paper and then erased it. If you don’t do a thorough job of erasing it, somebody may still be able to decipher what you’ve written."

In the case where tapes are damaged, however, such as from flight recorders recovered from plane crashes, the device could be quite useful. "This technology being kind of myopic—in other words it’s somewhat nearsighted—it’s actually very nice for small samples," explains Pappas. "So in case a tape was damaged and you only had small scraps of tape that you wouldn’t be able to play in a recorder, you’d be able to get whatever magnetic information is left there."

But tapes aren’t the only magnetic sources of information. As Pappas points out, the list of magnetic media is vast. For example, this type of data is on boarding passes for airplanes, answering machine tapes, cassette recorders, digital audio tapes, VHS tapes, and perhaps most ubiquitous of all—credit cards. With this technology, even cutting up credit cards into small pieces won’t destroy their information.

Right now, though, the technology is too time-consuming and costly to be used on a large scale or for evil purposes, according to Pappas. But he also says it makes good sense to cut up your credit cards into several pieces and dispose of them in separate trash cans.