A former French left-wing parliamentary candidate was arrested in southern France last week, over his tweets about a policeman killed during a jihadist siege.
Stéphane Poussier celebrated the death of Lieutenant Colonel Arnaud Beltrame, saying it was great and also adding that his death meant one less voter for President Emmanuel Macron.
Mr Poussier's Twitter account has since been deleted and French media say he could be charged with apologising for terrorism.
Colonel Beltrame died after being shot when a jihadist stormed a supermarket in Trèbes, southern France on Friday.