Gambian police have arrested a top official in the state intelligence agency over the murder of political activist Solo Sandeng in April 2016, a spokesperson said on Monday.
Sandeng's death in custody sparked a political movement that eventually ousted former leader Yahya Jammeh, who ruled the tiny West African nation with an iron fist for 22 years.
More than a dozen former agents of the National Intelligence Agency (NIA) face charges or are already on trial for the United Democratic Party organiser's murder after his arrest at an opposition protest.
Police spokesperson Superintendent David Kujabie said James Mendy, NIA head of security, was "in police custody and is being investigated in connection with the murder of Solo Sandeng".
A security source told AFP on condition of anonymity that Mendy was "one of the senior staff of the agency implicated in the murder".
Gambian prosecutors last week charged eight former spies with conspiracy to murder Sandeng while nine more, including its former chief Yankuba Badjie, are already on trial.
Two other former agents agreed last week to become prosecution witnesses.
Jammeh seized power in a bloodless coup in 1994, and was accused of rampant corruption and human rights abuses.
Sandeng's killing encouraged a weak and split political opposition to unite behind a single flagbearer, Adama Barrow, who went on to beat Jammeh in a December 2016 election.