The jurisdiction so ceded to the United States of America is granted upon the express condition that the Commonwealth of Pennsylvania shall retain concurrent jurisdiction with the United States in and over the lands and buildings aforesaid, in so far that civil process in all cases and such criminal process as may issue under the authority of the Commonwealth of Pennsylvania against anyone charged with crime committed outside said land, may be executed thereon in the same manner as if this jurisdiction had not been ceded. The United States shall retain such jurisdiction so long as the said land shall be used for the purposes for which jurisdiction is ceded and no longer.