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Article Title: Should Digital Evidence Be Stored In Perpetuity?
Author: Andrew Frowen
Category: Security, Information Technology
Word Count: 546
Keywords: computer forensics, acpo, digital evidence, hard drive deterioration, 
computer crime
Author's Email Address: [email protected]
Article Source: http://www.articlemarketer.com
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Where it is suspected that a computer has been used in the commission of a 
crime, the equipment is usually passed by law enforcement officials to computer 
forensic experts for analysis. In the event that any of the evidence extracted 
is successfully used to secure a conviction, the question then arises as to how 
long the evidence should be stored. 

Generally, there is a legal requirement to retain all forms of evidence unless 
the police seek permission to lawfully dispose of it, which is usually not 
granted until all avenues of appeal have been exhausted.

In the case of digital evidence, the reasoning behind this is quite clear: as 
new information or scientific methodologies come to light, it is possible that 
an appeal could be lodged, and the computer forensic analysts could be asked to 
go back and analyse the drive again.  

For example, in recent years, the 'Trojan horse defence' has developed where an 
accused person claims that a Trojan - a form of malware which allows third 
party control of a computer by an unauthorised person - was responsible for the 
illegal activity that has been proven to have taken place on their computer. If 
a convicted criminal were to appeal on these grounds, analysts would need to 
revisit the evidence to attempt to prove or disprove the presence of malware.

To ensure that evidence is not corrupted or contaminated during the analysis, 
the first stage of a forensic investigation is to create a 'forensic image', 
where an exact copy of the hard drive is created. It is this perfect copy of 
the drive that is analysed by computer forensic experts, while the original 
drive is moved to a secure storage area.

How long, then, should the original media be preserved, given that the forensic 
image is an exact and verified copy? The original, in most cases, would only be 
required if the validity of the forensic image was called into question. As a 
rule, this should not be an issue, since imaging must be carried out in a fully 
auditable fashion in line with the best practice guidelines for computer based 
evidence set out by the Association of Chief Police Officers (ACPO). However, 
in cases where a conviction carries a sentence of 20-30 years, it is possible 
that the original media could naturally degrade over time, rendering it 
inaccessible should an appeal be lodged on these grounds. 

For police high tech crime units and computer forensic laboratories, the 
natural deterioration of the digital media used to store the copied image is 
also a problem. A hard drive in regular use could be expected to last two to 
five years, with the potential to fail at any time, sometimes causing the 
permanent loss of the data held within it. While media containing copied images 
can be kept in heat and moisture controlled environments to limit degradation, 
there is therefore some question as to whether the fidelity of all data could 
be guaranteed for the full duration of a conviction. 

It seems then that new technologies will become increasingly necessary to 
fulfil the need for a long term storage solution for digital evidence. Until 
that time, there is always the real danger that evidence could be lost at the 
expense of the thorough investigation of a crime.

IntaForensics a BS EN ISO 9001:2000 registered firm providing Computer 
Forensics, Expert Witness, Mobile Phone Forensics, and Forensic Data Recovery 
to the Legal Sector, Police Forces, Local Authorities and Commercial 
organisations internationally. Visit http://www.intaforensics.com.
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