What is the purpose of having a model for investigations? How does it help the investigator or the student learning to b

[answerhappygod]

What is the purpose of having a model for investigations? How
does it help the investigator or the student learning to be an
investigator?
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Why is it necessary to calculate hash values on the primary
image made from a suspect’s hard drive? How many hash calculations
do you make?
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Throughout the investigation, a myriad of actions are performed.
At what point does the chain of custody begin, and how is it
relevant at each subsequent stage? (Remember to cite the
textbook page numbers where you find the answers)
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In what ways does Casey’s six-step model differ from the earlier
four-step models of digital investigation? What is new, and what
has changed?