My first post included a link to
another thread in which these exact scam patterns and names of scammers have been posted several times. You could have in fact saved yourself that money if you had googled the name "Slim Hollis" - you'd have been referred right to the GS thread I mentioned.
Of course the person is still contacting you - he'll try to get even more money out of you. This whole thing is a variety of the standard
"advance fee fraud" or 419 scam. You will most likely find out that most emails you've received can be traced to Nigeria, an adjacent country (sometimes Ghana or South Africa), possibly also to the Netherlands or the UK.
You can contact the police, but you are not likely to get any of your money back... Just stop responding to the scammers (and anyone who might contact you to get your money back - some scammers will raise your hopes that way and scam you out of even more money).
If you wish, I can point you to a few places and persons that know a lot more about these scammers - but they won't be able to get your money back, either.
Daniel