Q. Is there any connection between a shammes and a shamus?A. A shammes (or shammas) is an official acting as the beadle, sexton, and caretaker of a synagogue (from the Hebrew shammash, “to serve”).
What my dictionary says about shamus is “US slang: a police or private detective, probably from shammes, influenced by Irish Seamas, James”.
The origins of the shammes go back to Talmudic times. In those days his title was chazan, which did not denote a cantor but a synagogue overseer. He was a versatile individual with responsibility for the synagogue building, the conduct of services, the allocation of seats, the supervision (and sometimes teaching) of children, and even acting as court official and sheriff.
In time the offices of chazan and shammes were separated. The chazan chanted the services; the shammes became the general factotum whose duties ran from community administration to announcing lost property and proclaiming the results of law suits.
In old Anglo-Jewry, the beadle was regarded by some as a lowly servant, but this was far from the case in terms of his own self-estimation. In his own eyes, the beadle, with his top hat and robe and in some cases real livery and staff of office, was the real ruler of the synagogue. The wardens and ministers came much lower down and could not move an inch without his approval.
Even if the dictionary is right and the shamus derived from the shammes, there is a major difference between them in that the shammes would and could never leave the public gaze and go under cover.