The Madsen light machine gun begin used is one of the Madsens that were donated by the Brazilian Army to the State Police of Rio De Janerio; after army retired the Madsen machine gun in 1996. These guns were .30 cal weapons and were converted to fit 7.62 mm NATO.
Here close up of the Madsen in question:
From the picture it looks like an M1946, probably from Chile.