Neb. Rev. Stat. § 81-2029

No disability benefit payments shall be made except upon adequate proof furnished to the system of the existence of such disability, and during the time when any such benefits are being paid, the system shall have the right, at reasonable times, to require the disabled officer to submit proof of the continuance of the disability claimed. Disability is defined to be the complete inability of the officer, for reasons of accident or sickness, to perform the duties of an officer.