Mustapha Hamdan, who was shot attempting to flee a January 26 raid on the home of Sheikh Isa Qassim, died of cardiac arrest, Amnesty's Bahrain researcher Ariel Plotkin told AFP.
Plotkin said Hamdan had been brain dead as a result of the shooting.
Witnesses to the January shooting said police had raided Qassim's home in Diraz, a suburb of the capital Manama, where protesters had been regularly staging sit-ins after Qassim's citizenship was revoked.
Bahraini rights groups meanwhile blamed state security forces for Hamdan's death.
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The London-based Bahrain Institute for Rights and Democracy described the teenager's death as "an extrajudicial killing by the Bahraini government".
Home to the US Fifth Fleet, Bahrain has witnessed continuous unrest since 2011, when a string of protests inspired by the Arab uprisings erupted demanding an elected government.
Authorities in the tiny Gulf kingdom, ruled for more than two centuries by the Sunni Al-Khalifa dynasty, have consistently accused Iran of fomenting unrest in Bahrain.
Parliament this month voted unanimously to grant military courts the right to try civilians charged with any act of "terrorism".
Rights activists fear Qassim, currently detained over a string of charges linked to money laundering and illegal fundraising, could be among the first to face court-martial.
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