Section 24. An application for a license to engage in the private detective business or a license to engage in the business of watch, guard or patrol agency shall be filed with the colonel of the state police on forms furnished by him, and statements of fact therein shall be under oath of the applicant. Such application shall include a certification by each of three reputable citizens of the commonwealth residing in the community in which the applicant resides or has a place of business, or in which the applicant proposes to conduct his business, that he has personally known the applicant for at least three years, that he has read the application and believes each of the statements made therein to be true, that he is not related to the applicant by blood or marriage, and that the applicant is honest and of good moral character. The applicant, or, if the applicant is a corporation, its resident manager, superintendent or official representative, shall be of good moral character, and, unless such application is for a license to engage in the business of watch, guard or patrol agency, shall have been regularly employed for not less than three years as a detective doing investigating work, a former member of an investigative service of the United States, a former police officer, of a rank or grade higher than that of patrolman, of the commonwealth, any political subdivision thereof or an official police department of another state, or a police officer in good standing formerly employed for not less than ten years with the commonwealth, or any political subdivision thereof or with an official police department of another state.