The man, a 35-year-old Chinese citizen, was arrested earlier on Wednesday for using a false document, a felony.
He is also suspected of violating the Maritime Act for lack of seaworthiness.
It is not grounds for detention because the penalty does not amount to one year, Combier-Hogg says, adding that the commander denies any crime.
The tanker Jin Hui was boarded at 2 p.m. on Sunday south of Trelleborg in Swedish territorial waters.
According to Carl-Oskar Bohlin (M), Minister for Civil Defence, the ship is suspected of being part of the Russian so-called shadow fleet and is on the sanctions lists of the EU, UK and Ukraine.
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