Rudolph's cousin Marie Larisch in her My Past (available online for free) did mention I believe the bronze ring -- either that or in one of her other writings.
There's very few original first hand experiences written into books about this subject -- and if they differ from the official version tend to be ignored.
From Tales from the Vienna Woods: The Man who would have been Emperor
In retrospect, after viewing the horrendous world events which followed, it now seems more than
reasonable that, for political reasons, a third party or parties committed the murders, killing Vetsera
simply to silence her and to cover up the political nature of a criminal assassination. It appeared that
Marie had been killed several hours before Rudolf, and perhaps he was forced to watch her brutal,
quietly inflicted death, which forensic analysis generally concludes was probably from beating, not
gunshots. Furthermore, Rudolf's alleged "suicide letter" to his wife could have been written under
duress. In it, he bids farewell to her and his friends, saying that "only death can save his good name",
but it does not give a reason why he killed himself, and in fact makes no mention of suicide or of
Marie. In any case, how would a double-suicide or murder-suicide "save his good name"?
Evidence in reports made at the time of the deaths stated that his body showed evidence of a major
violent struggle. The body of the Crown Prince wore gloves at his funeral and his mother was not
allowed to see his hands, since they were supposedly injured and possibly covered with defensive
wounds. This also resembles what Empress Zita said about the events. All the same, the exact cause
and circumstances of Rudolf's death remain a mystery to this day.