Video shows the man entering St. Agnes Cathedral in Rockville Centre, prying open the church's donation box, and removing cash on August 20 and again on August 27.
Authorities say it is unclear how much cash he stole.
Police describe him as a white or possibly Hispanic male with a thin build, approximately 5-foot-9 with medium length brown hair.
Anyone with information can submit an anonymous tip to Nassau County Crime Stoppers or call 1-800-244-TIPS.
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