(CNN) -- A Somali man who authorities say is the highest-ranking pirate ever brought to the United States for prosecution was given 12 life sentences Monday by a federal judge in Norfolk, Virginia.

U.S. Attorney Neil MacBride said he hopes the severe sentences send a clear message to other would-be pirates to stay away from U.S-flagged ships in the Gulf of Aden and off the coast of Somalia.

The sentences handed to Mohammad Saalli Shibin -- who authorities say negotiated for the release of pirate-held hostages and vessels in return for ransom -- follow his involvement in arranging ransoms for two dramatic, high-profile pirated vessels.

In one case four Americans were shot to death aboard their yacht in February, 2011, while negotiations with the U.S. military were proceeding. In the other case, 22 crewmen aboard a German-owned vessel were allegedly tortured following their hijacking, and the pirates received a ransom of more than $5 million.

During the sentencing, the judge found Shibin responsible for the entire ransom and ordered him to make restitution for more than 5.4 million dollars.

The sentencing followed guilty verdicts against Shibin on 15 counts including piracy and kidnapping in April, 2012. That came just about one year after Shibin was captured in a raid in Somalia by Somali forces working with the FBI.

During negotiations for the four Americans, Shibin remained on shore and determined the size of the ransoms to be demanded, and he did not board the yacht himself, authorities said. Three other alleged pirates charged with the deaths of Americans Jean and Scott Adam of California, and their friends Bob Riggle and Phyllis Macay of Seattle, are scheduled to go on trial and will face potential death sentences.

Federal prosecutors in Norfolk have prosecuted 18 Somali pirates to date.