All too frequently a peer will contact me in a panic about recovering deleted files from a suspect's hard drive--after my peer has trampled on the digital evidence like a rookie police officer at his first crime scene. Often valuable evidence is lost for good,or unusable in court; or worse, the suspect knows he is being investigated.
With the proper hardware that you probably already have and freeware available online, you can easily build your own basic computer forensics lab that will hold up in court, reduce E-Discovery costs and, most importantly, retrieve valuable evidence for all your investigations.
See also: How to Plan an Investigation
Here is the cardinal rule at the beginning of any forensic investigation: Don't touch the suspect's computer or hard drive.
On television you see detectives and CSI staff walk into a crime scene, log onto the suspect's computer and start looking for evidence. Do not do this. Ever. Any touch of the keyboard, or mouse, or even the simple act of powering the computer down, forensically changes the hard drive.
These are the two critical steps you must take first:
First, when you approach a suspect's computer unplug from the back of the computer (not the wall) and let it die. Powered-on laptops should have their battery removed to shut the system down. This sudden shutdown freezes the hard drive's evidence in place.
Second, never attempt to view the suspect's hard drive without a read/write blocking device. Read/write blocking devices prevent your computer from altering the suspect's hard drive while you are looking for evidence.
Without these two steps in place your evidence will have a tough time holding up in court. For more information on digital evidence collection check out the Secret Service's Best Practices For Seizing Electronic Evidence, Pocket Guide for First Responders [PDF link].
With those rules clear, nothing should hold you back from building a basic setup to forensically image your suspect's computer (i.e. create a duplicate copy of it) and review it for evidence.
The first step before gathering evidence is reconnaissance. In advance, find out the make and model of your suspect's computer. Most businesses use stock systems, so knowing your suspect's computer model number can help you determine the type of hard drive (SATA vs ATA), its size (40GB and beyond) and--most importantly--how to access and unplug the hard drive. Computer makers are getting creative with cramming hard drives into odd spots, so a simple search for Dell Latitude D400 hard drive on YouTube or Google may help you quickly and easily remove the drive.