An Islamic extremist, 31, was arrested Monday for the murder of Tunisian opposition politician Chokri Belaid.
"The police arrested a Salafist suspected of killing Belaid," a senior security source told Reuters without giving more details.
Media reports suggested a second man, an alleged accomplice who drove the getaway motorbike, was also arrested Monday, and both were members of the radical Muslim Salafist movement, AFP reported.
AFP reported the alleged killer was a furniture maker who lived in a nearby suburb.
They said the arrests were carried out on the strength of the testimony of a woman who had witnessed the killing. She is under police protection.
Chokri Belaid, leader of the Unified Democratic Nationalist party, was shot by a hooded gunman at close range outside his home in the capital by a man who fled on a motorcycle on February 6, The Guardian reported.
The 48-year-old died in hospital shortly afterwards.
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His death triggered days of political unrest across Tunisia and his funeral saw clashes between police, mourners and hard line Islamists.
The funeral brought the largest gathering in Tunis since the revolution two years ago, London's Telegraph reported.
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The violence erupted outside the cemetery when gangs of men threw rocks and attempted to steal cars, forcing police to fire tear gas.