The FBI is searching for the mother of the Minnesota gunman who killed two children, saying she has refused to cooperate with the investigation.

Federal agents descended on an apartment belonging to Mary Grace Westman in Florida on Wednesday, after her son, Robin Westman, opened fire at the Annunciation Church in Minneapolis.

Footage captured by local news showed three plainclothes members of the FBI knocking on the front door of the building in East Naples and shouting for a “Miss Westman”.

The individuals, who are casually dressed and wearing sunglasses, are then seen returning to their car empty-handed.