Is there a possibility to get special software to permanently delete,deleted files from the system.What I mean by that is like the forensic units from the police,what program do they use to retrieve the necessary information that they need.

For example : if there's a case about child pornography,and the suspect deleted the files from the computer they can retrieve the files on your hard drive although it was deleted.


Thank You

Yes and no.
Forensic units use specialised software to recover this information.
The best you can do would be to use military grade file shredding, this is based on OLD, publicly available algorithms.

secure file shredder - Google Search (http://www.google.co.uk/search?hl=en&client=firefox-a&channel=s&rls=org.mozilla:en-GB:official&hs=ziM&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=secure+file+shredder&spell=1)