MINEOLA - Police are investigating the death of a Nassau police officer who officials say was shot down by a fellow officer.

Nassau County officer, volunteer firefighter, husband and father of two young boys Geoffrey Breitkopf is being remembered today by family and friends.

Breitkopf was responding to a scene Saturday night where police say a 21-year-old self-proclaimed Satanist, Anthony DiGeronimo, was wielding a knife around his Massapequa Park neighborhood. DiGeronimo was shot and killed by police inside his home.

Breitkopf, who was a part of the Bureau of Special Operations Unit, was responding as a plain-clothes officer to the scene when he arrived after the shooting.

PBA President James Carver says a civilian witness yelled out "gun, gun" as Breitkopf approached the scene with his police badge around his neck and his department-issued rifle at his side.  Carver says that is when the MTA officer opened fire.

According to the Nassau County PBA, Breitkopf's wake will be held this Wednesday and Thursday between 2 p.m. - 5 p.m. and again from 7 p.m. - 10 p.m. at the Selden Fire Department headquarters. 

His funeral Mass is scheduled for Friday at 12 p.m. at St. Margaret's of Scotland in Selden.

Police: Nassau cop was accidentally shot by another officerOfficer dies in Massapequa Park shooting