This is an expanded version of the article that appeared in the October 2008 issue of Law Officer magazine.
No matter what kind of law enforcement you're involved with, most of your evidence is going to be documentary in nature. Reports, statements, court documents, diagrams, photographs, video and audio recordings, on and on, are going to describe what happened and who it happened to. How do we preserve all of this?
There are warehouses full of banker's boxes, which are in turn filled with paper, photos, tape recordings, film negatives, and other "primary source" documents. These exist because many jurisdictions have no statutory rules on how long such evidence must be maintained, and because some of those cases are either unsolved or the people responsible for them are still incarcerated and have the very slim chance their cases will be re-opened.
Paper records can be reduced to more space-efficient media, such as reel-type microfilm or microfiche, but the preferred method these days is to scan the records into digital form and preserve them on some type of magnetic or optical media. This is feasible with everything that isn't physical evidence itself, such as forged documents and suicide notes. Hard disc storage is increasingly cheaper in terms of dollar-per-gigabyte, and has the advantage of being readily accessible. But all hard discs are mechanical devices that will eventually fail, and a crashed disc drive will take most of its data with it unless you're willing to go heroic and expensive measures to recover it. Various forms of disposable magnetic media, e.g. floppy discs, are limited in both capacity and durability, as a refrigerator magnet can render them useless. Despite the billions of these produced, it's now rare to see a new computer sold with a drive capable of reading them.
Full serve or self serve?
If you have a backlog of paper reports, photos, recordings, etc. to be archived, your first decision is whether to handle this yourself or farm out the work. This decision is usually based on your budget, but the size of the backlog should be a critical factor as well. If you really do have a garage or warehouse full of documents, you don't even want to think about doing this yourself.
Commercial enterprises like Laserfiche (www.laserfiche.com) offer turnkey solutions to document management, with several levels of service. They can not only convert your backlog to digital form, but make every document searchable and retrievable online, tie case information such as recurring names or addresses together, and provide systems with audit trails and access levels for almost any size organization.
When you don't want to get into anything quite that ambitious, there are several prison industries that handle conversion of paper documents to digital form. You may shudder at the thought of handing over your case files to convicted felons, but the corrections professionals who manage these operations are well-versed on what kind of jobs are appropriate for their inmate labor force. PRIDE (Prison Rehabilitative Industries and Diversified Enterprises) Enterprises, operated under the Florida Dept. of Corrections, has such a service.
If you're still intent on keeping this an in-house project, some strategic planning is critical. The Portable Document Format (PDF) standard created by Adobe (www.adobe.com) has become all but universal for document archiving and exchange. It's highly versatile, allowing users to incorporate text, photos, sounds, video, and most other computer-based media into a single file. It offers a high level of security. PDFs can be digitally "signed" using a registered certificate that no one but an authorized user can apply. If the document is altered in any way, the "signature" will become void and betray the change. PDFs can also be encrypted so that only users with the appropriate authorizations can open and view them. Adobe distributes its free Reader software (there is probably a copy on your computer) so that anyone can view a PDF, and there are several software applications other than Adobe Acrobat that can create and edit PDFs.
For the creation of many documents that are going to include diverse types of media, you're best off to stick with the native Adobe Acrobat software, and to have someone who understands it thoroughly overseeing the project. Like many software packages, using the basic features is easy, but it takes some expertise to make use of the lesser-known aspects. Invest in some training for the project manager. Adobe includes a directory of training courses on their web site (www.adobe.com/training/).
You will also need to invest in an industrial-strength sheetfed scanner to convert your paper documents into digital form. A sheetfed scanner is similar to a copy machine, but with an Automatic Document Feeder (ADF) attached. The models at the office supply store are fine for occasional use, but they won't be up to the task of scanning hundreds or thousands of pages a day. Desktop-quality scanners will have ADFs with a capacity of maybe 50 sheets, and they're prone to jamming and feeding of multiple sheets when the paper quality is anything less than perfectly flat and pristine. Models like the Kodak i250 and Fujitsu fi-4530c have ADFs that will hold 100 or more sheets and process 30 or more pages per minute.
Other media and filing strategies
Archiving photos, video clips, and sound recordings require similar planning. All can be embedded into a PDF, but they'll first have to be converted into a form the PDF can use. Digital photos are easy--they're already in computer-compatible format. How you will go about conversion of sound and video files is dependent on what form they're in to begin with. Getting an interface that will allow your cassette recorder or VHS tape player to "talk" to your computer and create suitable files may only take a trip to Radio Shack. If you don't have anyone on your staff who understands how to get one media format into another, make a call to the AV department at a local college. Colleges have endured many changes in the formats of instructional materials and the people in these departments can be very knowledgeable and helpful.
You're building a library of information, and if you don't have a filing system or "card catalog" (for those of us who remember when they consisted of actual cards), you'll never find what you need. A digital photo may have started life as "DSC012595.jpg," but it doesn't have to stay that way. Windows allows for 255 characters in a file name, and 255 levels of file folders. With a little forethought, you can make those file names line up in a useful order. Dates in the format YYYY-MM-DD (e.g. 2008-09-01) will automatically sort in date order. A folder hierarchy might start with the year, with subfolders for each month, then subfolders within those for each day or each case number. Within these, there can be subfolders based on content type (Reports, Statements, Subpoenas, Search Warrants, Photos, Video, Sound), badge number, division, or whatever other system you prefer. Photo files can be descriptively renamed such as "crime_scene-exterior-south_lawn-footprint-DSC012595.jpg". Although Windows allows spaces in file names, not all software applications (like web browsers) do. Therefore, it's best to connect words in phrases by underscores and phrases by dashes. Don't rely on uppercase vs. lowercase letters, as Windows doesn't distinguish between the two for the purpose of file names.
Optical media such as CDs and DVDs have become the preferred method of archival storage. This is the case with our data as well as our entertainment media. Movies, music and games are distributed on CDs and DVDs that are identical in form factor, inexpensive, and easy to store. Because these discs are unaffected by magnetic fields and reasonably durable, we've become mostly complacent that they will outlast us. Sadly, this may not be the case.
Libraries and other institutions with some experience in long-term storage of optical media are finding that some of their collections have fallen victim to "laser rot," where the optical media deteriorates to the point that the data contained on it is no longer recoverable. Dinosaurs such as myself recall when "compact discs" were new, but in fact they have been with us since 1982, when the first music CDs were produced. Since then, there have been many versions of the format, mostly to allow for larger amounts of data on the disc. Basic computer and audio CDs hold about 700 MB of data, where the latest Blu-Ray versions can hold over 50 GB--over 70 times as much--of information. This means that more information is being recorded to media that can fail and take the entire record with it.
Optical disc composition
A standard CD has four layers. The lowermost layer (the one closest to the laser) is polycarbonate, a rigid plastic that is very strong, but prone to scratching. Above this is a metal reflective layer that is usually aluminum, but sometimes made of gold. This layer contains the tiny pits and lands that are read by the laser and translated into the ones and zeros that make up binary data. Above this is a coating of lacquer that protects the metal layer, and a label goes on top.
Commercial DVD and audio discs are mass-produced with a "glass master" and metal die that is physically pressed into the metal layer before the lacquer is applied. Recordable CDs, or CD-Rs, incorporate a dye into the metal layer that allows a relatively low-power "write" laser in a desktop computer drive to record information onto the CD by changing the color of the dye and allowing the "read" laser to see the underlying metal layer. There are three types of dyes in common use: phthalocyanine (light green), cyanine, and azo (both are varying shades of blue). The type of dye used has a lot to do with the long-term stability of the CD.
Rewriteable CDs, also called CD-RWs, use a metallic alloy instead of a dye. The write laser in a desktop computer drive changes the degree of reflectivity of the alloy, creating the data pits. CD-RWs can be re-written, where CD-Rs are one-write, non-editable media. The metallic alloy changes in CD-RWs are not as legible as the data on commercial and CD-R discs, and some older desktop drives can't read CD-RW discs. Because the data on CD-RWs is not as robust, it is more susceptible to degradation through aging.
DVDs are even more complex, being two discs bonded together back-to-back. The polycarbonate substrate for each disc is half as thick as with CDs. DVDs can also have dual data layers on each side, producing several varieties: single layer/single side, single-layer/dual side, dual-layer/single side, and so on. DVDs also come in recordable and recordable/rewritable (DVD-R and DVD-RW) formats, using processes similar to their CD counterparts. DVD-R/RWs don't seem to come in phthalocyanine versions, though.
Testing methods and results
The Canadian Conservation Institute in Ottawa conducted an accelerated aging study of optical discs after discs in Canadian library collections were unreadable and in some cases visibly degraded.
The aging tests were performed using a chamber where temperature and humidity were carefully controlled. The samples were subjected to 80 degrees C at 85% relative humidity for four intervals of 500 hours (21 days) each. Before and after each cycle, the discs were allowed to adjust slowly to the change in moisture and temperature. Rapid changes in environment can cause the polycarbonate substrate to warp and expose the other layers to water droplets.
Some of the CDs fell victim to delamination of the component layers, where the layers separated. This was probably due to poor sealing of the outer layers of the discs at the time of manufacture. Some of these were probably the product of inferior quality controls when the production processes were not as refined as they are today. Still, 15% of the discs of more recent manufacture also delaminated during the accelerated aging tests.
Fading of the dye layers was much worse with the azo and cyanine dyes than with the phthalocyanine. The cyanine discs had severe fading 25% of the time, and the azo discs 60% of the time. Fading of the dye layer alone does not make the discs unreadable, but it contributes to the problem. Of the phthalocyanine discs, 84% could still be read after the aging tests, but the number of readable cyanine discs fell to 20%, and none of the azo discs could be read completely.
The DVD-Rs and DVD-RWs also performed badly in the aging tests. Only 8% of the DVD-Rs were still readable after 500 hours of aging, and none of the DVD-RWs were.
The brands of discs tested covered the spectrum from budget labels like Smart Buy and Imation to premium sellers such as Verbatim. In every case, the type of dye and the disc format was more predictive of durability than cost or brand name. CD-Rs with phthalocyanine dye were far more resistant to temperature and humidity than any other type.
When you go shopping for CD-Rs you'll use to save your files, don't expect that the salesperson will know which dye is used. If you ask him anything that includes the word "phthalocyanine," he'll probably interrupt with "gesundheit." Instead, look at a sample and see what color the underside is. You want to see green, not any shade of blue.
Labeling the discs also has its hazards. There is only a thin layer of lacquer between the label and the metal foil of the disc, and ink can seep through and contaminate the foil. For this reason, writing directly on the disc (especially with dense, permanent ink such as that in Sharpie marking pens) is discouraged. Full-coverage paper data labels are an unnecessary expense, and they can be trouble if their adhesive fails or the label is applied off-center. A small strip of labeling tape on the label side is unlikely to do much harm, but consider whether the adhesive on the label will endure time, temperature and humidity, too. As a backup, also label the envelope or case used to store the disc.
Data can be written to discs at varying speeds. It might save a little time to write the discs at 40X speed, but faster write speeds are more prone to errors. Keep your write speeds to around 8X or less, and set the disc-writing software to check and verify every disc for data integrity. Make two copies of every disc, and store them separately--ideally, one at an off-site facility with good humidity and temperature controls.
Once the backlog is archived, keeping up with new documents is relatively easy. However you go about archiving your records, do it carefully and systematically, and remember that you're preserving history whose importance may not be known for many, many years.
Iraci, Joe. The Relative Stabilities of Optical Disc Formats. Restaurator 26: 124-150 (2005).
Shahani, Chandru. Longevity of CD Media. Research at the Library of Congress (2003).