Not a prosecution, but a congressional hearing concerning JFK's grandfather. It is my understanding that the records of the proceedings were recently unsealed. Does anybody know if they are online, or otherwise available?

wikipedia:

In 1918 Tague was faced with a major challenge from ex Boston Mayor John F. Fitzgerald. Tague lost the 1918 primary election to John F. Fitzgerald, by 50 votes.^[7] Tague contested his loss in the primary and appealed that loss to the election commissioners, but he lost that appeal and Fitzgerald was declared the nominee of the Democratic party.^[8] Tague contested the election as a sticker and write in candidate and initially Tague narrowly lost the general election to Fitzgerald^[9][10] by 238 votes^[11]

Tague contested the election. On October 2, 1919, by a vote of 5 to 2, the House of Representatives elections committee voted to unseat Fitzgerald and to seat Teague.^[12]

After the House committee canvassed over 1,300 votes Fitzgerald's plurality went down to 10 votes. After determining that one third of the votes in three precincts of Boston's Ward 5 were fraudulent the House of Representatives committee threw out the votes of those precincts. The committee determined that the election had been tainted by illegal registrations and fraud.^[11] The committee determined that Tague won the election by 525 votes.^[11]On October 23, 1918 the full House of Representatives unseated Fitzgerald and seated Teague.^[13]