Alfred Gadenne, 71, was found dead on Monday in a cemetery where he opened and locked the gates every day, near his home in Mouscron, near the French border.
Local media said the suspect is an 18-year-old who attacked the mayor to avenge his father, a former town employee who was sacked and committed suicide in 2015.
The case sparked strong emotion on Tuesday in Belgium. Prime Minister Charles Michel on Twitter said he learned "with alarm" the death of Gadenne, who he said was widely liked by all.
Martine Aubry, the former French Socialist party leader and long-time mayor of neighbouring Lille in a tweet said she was "horrified" by his death.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
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