The sources for the book seem to be the census of the hamlet of Djupivogur from 1802 onwards and some "memoranda of transactions with customers, stock taking, and other aspects of his work" that survive. The memoranda I think is the complete books of the general store that are archived in the National Archives, Reykjavik. The book has some photos [2] - his very fancy signature is quite legible.
It says he is mentioned many times in the census: as a mate on a sailboat (possible owned by the store) in 1804, a donation to the poor he made in 1808, registered as an assistant and workman, in a district council meeting in 1810 his assets were recorded as "a ewe, three yearling lambs, and a horse", then no records until 1815, and by 1817 he owned two boats. The census listed him as a freed slave from Kantitusjanhill, St. Croyx since he was honest about his background.
That's about as far as I read. My impression is that it’s more of a pop-history book than a painstakingly sourced academic tome. Lots of “probably” and “must have” speculation.
[1] https://press.uchicago.edu/ucp/books/book/chicago/M/bo219363...
Wow, it's fascinating they still have those.
Here is the relevant open-access editorial published in Nature Genetics: https://www.nature.com/articles/s41588-018-0049-4
And the research article "Reconstructing an African haploid genome from the 18th century" (which is unfortunately neither open-access nor available on PubMed Central.... perhaps this article also needs to be "freed") : https://www.nature.com/articles/s41588-017-0031-6
Bone-chilling.
It’s entirely possible that the court had noticed exactly that, and spelled it out as clearly as it was legally able without actually writing ‘here, have a fifteen day head start!’