The Rooswijk was located by a local diver who dived the wreck many times before the sands shifted exposing chests of silver ingots and coins.
He went about it properly contacting the UK Receiver of Wrecks who put him in contact with the Dutch Government who own the wreck after the demise of the VOC.
The Dutch had a long standing agreement with Rex Cowen, who put together a professional recovery team of divers working under the supervision of a experienced marine archaeologist to cary out a rescue archaeology project financed by goodwill and donation and by a percentage split of the silver (after recording) with all the other artefacts going to Dutch Museums.
The silver was recovered and the split was made with a Dutch frigate and government minister going to Plymouth UK to pick up the Dutch share.
English Heritage who only learnt of the operation after the operation, then placed a Protection Order on the wreck preventing any further excavation even though the Dutch Government as owners would like to continue with the excavation as it is probably the most complete assemblage of VOC artefacts from any VOC wreck anywhere in the world.
Water depths are generally less that 75 feet.
Further info can be found by downloading the two pdf's (righthand side) on this web site:
http://www.english-heritage.org.uk/discover/maritime/map/rooswijk/
With regards to the coins many got sold legally at auction in the states, that can also now be found for resale on eBay and at specialist dealers, but make sure you get a valid certificate of authenticity and ask what auction it was purchased at, as as far as I know they were not sold for disposal privately in the states ( but I could be wrong).
In the Uk I can vouch for the eBay seller under the name of Awerty ( search under "shipwreck") for shipwreck coins, as he has a long association (no pun intended for the ones that get it) with the business and I have bought from him in the Isles of Scilly over the years and as he is a friend of Rex Cowen has sold many Rooswijk coins over the years.
VOC