All appointments to sworn police positions above the rank of trooper within the Department of State Police shall be made by the Superintendent of State Police from among the sworn police officers of the Department, except for those positions designated in subdivision A 20 of § 2.2-2905, or whenever the Superintendent determines, in writing, that a position requires knowledge, skills, or abilities such that a sufficient pool of qualified candidates does not exist within the Department of State Police. It was and is the intent of the General Assembly that the primary factor in the career progression program is satisfactory years of service.