Upon retirement of a City policeman or fireman because of injuries sustained in line of duty and in cases where such disability is continuing, he may informally petition the Board for the services or payments herein provided. Such petition may be by a letter or other document referring the Board to his departmental case. Upon receipt of such petition, the Board may:refer such matter back to the department from which the claimant has been retired for full investigation and prompt report to the Board; or refer such claim to any other agency of the City, including the Law Department for investigation by its Central Bureau of Investigation. Upon receipt of such report, the Board shall act in disposing of the claim before it. In doing so it may act solely upon the record before it or it may call the claimant and other witnesses to aid in its determination of such matter. Where there is a dispute as to whether a retiree’s medical condition is service-connected and should be compensated under this section, a decision of the Board after full investigation shall be deemed final and conclusive. City Code, 1976/83, art. 1, §138(d) Ord. 70-885