Durn waited until the rest of the public left, then started shooting.
He was hit at point-blank range as he stood with his back to Durn.
Stephanie Durn, 68, said her son had spoken "maybe 20 times" about wanting to kill.
Durn is a gun club member and hardline green activist with a history of mental illness.
CRAZED killer Richard Durn wanted to gun down all 53 of his local councillors, prosecutors said last night.
Durn, 33, shot dead eight council members in Nanterre, Paris, and seriously injured 19 more early yesterday.
One of Mr Rijik's colleagues, Catherine Maurel, said victims' families were devastated that Durn would never face them in court.
Mr Durn plunged from the roof into the courtyard below.
Durn had also lost a shoe, possibly in the struggle with police.
But the dominant view was that Durn had killed himself.
Durn, 33, was being interrogated at the French equivalent of Scotland Yard when he plummeted from a fourth- floor skylight.
, 33, jumped suddenly towards a fifth-floor window at the Paris headquarters and struggled out of the grasp of two officers who tried to pull him back inside, police said.