Hi Janet, I would try and research in newspapers. There's free and paid databases of them. It's very likely that somebody wrote an article about what had happened. If you know the region/city where Robert Bruce lived, before he was imprisoned, I'd suggest you'd start there, using the name of the city and region. With an online newspaper search.
Dear Ms. Blowers,
Thank you for posting your request on History Hub!
In addition to the information from the previous posters, we suggest that you contact the Rhode Island State Archives and the The Rhode Island Historical Society for prison records from the Rhode Island State Prison and the Sockanosset Boys School.
We hope this is helpful. Best of luck with your family research!