The following is from the Gentleman’s Magazine, November 1767, page 559
“The famous Higgins was executed at Carmarthen. He did not make that resistance he threatened. He died in a very sullen humour, confessed nothing, but, as he mounted the ladder, he gave the sheriff a letter, which he desired might be sent by express. A particular account of this extraordinary robber shall be inserted in the supplement.”
I am still looking for the supplement, but a more detailed account is in The London Magazine or Monthly Intelligenser.