Here's an article ("Hunt for stolen crown jewels failed to solve great mystery") filed last year by Ralph Riegel in The Irish Independent about the unsolved theft of Ireland's 'crown jewels' stolen almost a century ago (today's date marks not the date of the actual theft but the date of discovery of the loss).
... The gems were stolen from a safe in Dublin Castle on July 6, 1907, in arguably Ireland's most famous robbery... The gems, valued in 1983 at over IR£2m, have a current value of around €14m. They were donated to Ireland by King William IV in 1830 to be used on ceremonial occasions by the Order of St Patrick. They were stored in a special safe in the library of the Office of Arms in the Bedford Tower of Dublin Castle. However, the safe was not installed in a special strong room because the room was accidentally constructed with too narrow an entrance to allow it to be fitted. The gems were dramatically stolen in 1907 just days before King Edward VII was due to begin a state visit to Dublin. The theft was hugely embarrassing, both for the Royal Irish Constabulary and the Dublin Castle authorities, because King Edward was due to invest Lord Castletown as a knight in the Order of St Patrick. Even more embarrassing was the fact that the Dublin detective headquarters was located barely 100 yards away. ...From the National Archives is a description of the jewels:
The regalia of the Order of St Patrick – the so-called “Crown Jewels” were kept in the Office of Arms in the Bedford Tower in Dublin Castle. The jewels consisted of the insignia of the Grand Master of the Order of St Patrick (the Lord Lieutenant) and the collars and badges of the Knights of St Patrick. The insignia of the Grand Master comprised a star and a badge. The jewels forming the star consisted of Brazilian diamonds with eight star-points with a central shamrock made of emeralds and a cross of rubies in the centre on a background of blue enamel. The badge also had emerald shamrocks and a ruby cross surrounded by blue enamel and rose diamonds and within Brazilian diamonds. The jewels been the property of Queen Charlotte, then of King George IV and finally of King William IV. This king thought that they would form fine ceremonial decorations for the Order of St Patrick and the Lord Lieutenant of Ireland to wear on ceremonial occasions and so he presented them to the Order in 1830. In 1907, these jewels were valued at £33,000.You can read the National Archives' "The Theft of the Irish 'Crown Jewels'" for more details.
In 2008, Francis Shackleton Jr.'s name came forward as the prime suspect in the theft.