N.J. Stat. § 43:16A-11.9
Any member of the Police and Firemen's Retirement System of New Jersey who has at least 20 years of creditable service in the retirement system and who leaves a position covered by the retirement system, with the approval of the employer, to take a full-time position with a. a federal agency, b. an agency of another state or local government thereof, c. a national, regional, statewide, areawide or metropolitan organization representing member state or local governments, d. an association of state or local public officials, or e. a nonprofit organization which has as one of its principal functions the offering of professional advisory, research, educational or development services, or related services, to governments or universities concerned with public management, may, upon filing an application with the board of trustees of the retirement system, purchase credit in the retirement system for all or a portion of the time of service with the public agency or private organization, but not exceeding three years, as provided in this act.
The member may purchase credit for the service by paying into the annuity savings fund the amount determined by applying the factor, supplied by the actuary, applicable to his age at the time of the purchase, to his creditable salary in the last 12 months of creditable service in the position covered by the retirement system immediately preceding the service with the public agency or private organization. The purchase may be made in regular monthly installments or in a lump sum as the member may elect and pursuant to rules and regulations as may be promulgated by the board of trustees. The member shall bear the entire cost for the additional retirement benefit attributable to the purchased credit. If, upon retirement, the member's payment for purchase of the credit is insufficient to provide for the additional retirement benefit attributable to the service, the difference may be assessed to the member, or a pro rata credit may be granted based on service purchased prior to the date of retirement, at the election of the member.
If the member retires prior to completing the purchase, he will receive pro rata credit for service purchased prior to the date of retirement, unless he makes an additional lump sum payment at that time as will be necessary to provide full credit.
The purchase may be made within four years of the date of the member's last contribution to the retirement system in the covered position immediately preceding the service with the public agency or private organization.
N.J.S. § 43:16A-11.9