He was appointed Ulster King of Arms in 1893, but was removed from the post in 1908 following the theft of the Irish Crown Jewels in the previous year.
In a letter dated 2 October 1892 Vicars's half-brother Peirce Mahony wrote that Sir Bernard Burke, Ulster King of Arms, was dying and urged him: "You should move at once.
This work became very valuable to genealogists after the destruction of the source material for the book in 1922 when the Public Record Office at the Four Courts was destroyed at the start of the Irish Civil War.
They were found to be missing on 6 July, and a Crown Jewel Commission under Judge James Johnston Shaw was established in January 1908 to investigate the disappearance.
The substance of the article was that Vicars had allowed a woman reported to be his mistress to obtain a copy to the key to the safe and that she had fled to Paris with the jewels.
According to the communiqué issued from Dublin Castle, thirty armed men took him from his bed and shot him, leaving a placard around his neck denouncing him as an informer.
The proclamation given under Martial law and ordering their demolition also stated: For any outrage carried out in future against the lives or property of loyalist officials, reprisals will be taken against selected persons known to have rebel sympathies, although their implication has not been proved.