The theft from Dublin Castle of the Irish Crown Jewels, the heavily jeweled star and badge regalia of the Sovereign and Grand Master of the Order of St. Patrick, as well as the collars of five knights of the Order is discovered on July 6, 1907. The theft has never been solved and the jewels have never been recovered.
Prior to 1903, the insignia of the Sovereign and those of deceased Knights are in the custody of the Ulster King of Arms, the senior Irish officer of arms, and are kept in a bank vault. In 1903, the jewels are transferred to a safe, which is to be placed in the newly constructed strongroom in Dublin Castle beside the Ulster King of Arms’ office. The new safe is too large for the doorway to the strongroom and Arthur Vicars, the Ulster King of Arms, instead stores it in his office. Seven latch keys to the door of the Office of Arms are held by Vicars and his staff, and two keys to the safe containing the insignia are both in the custody of Vicars. Vicars is known to regularly get drunk on overnight duty and he once awoke to find the jewels around his neck. It is not known whether or not this is a prank or a practice for the actual theft.
The insignia are last worn by the Lord Lieutenant, Lord Aberdeen, on March 15, 1907, at a function to mark Saint Patrick’s Day on March 17. They are last known to be in the safe on June 11, when Vicars shows them to a visitor to his office. The jewels are discovered to be missing on July 6, four days before the start of a visit by King Edward VII and Queen Alexandra to the Irish International Exhibition, at which it is planned to invest Bernard FitzPatrick, 2nd Baron Castletown, into the Order. The theft reportedly angers the King but the visit goes on as scheduled, however, the investiture ceremony is cancelled.
A police investigation is conducted by the Dublin Metropolitan Police (DMP). Posters issued by the DMP depict and describe the missing jewels. Detective Chief Inspector John Kane of Scotland Yard arrives on July 12 to assist. His report, which is never released, is said to name the culprit but is suppressed by the Royal Irish Constabulary (RIC).
Vicars refuses to resign his position, and similarly refuses to appear at a Viceregal Commission into the theft. Vicars argues for a public Royal Commission instead, which has the power to subpoena witnesses. He publicly accuses his second in command, Francis Shackleton, of the theft. Kane explicitly denies to the Commission that Shackleton, brother of the explorer Ernest Shackleton, is involved. Shackleton is exonerated in the Commission’s report, and Vicars is found to have “not exercise[d] due vigilance or proper care as the custodian of the regalia.” Vicars is compelled to resign, as are all the staff in his personal employ.