He started as a singer, but his fledgling musical career was interrupted by the German invasion of 1940.
In 1943, he joined the Sûreté nationale as Inspector to avoid being shipped to a forced labour detail.
Assigned to hunt the Resistance, he instead helped partisans escape from occupied France.
Borniche's investigations depended on informants and on French records that required anyone staying at a hotel or renting a room to give their name and identity card number.
He was able to bargain with informants by offering them a signed permit to remain in Paris (despite being banned from the city by other police forces) and by delaying distribution of official warrants by keeping the notices locked in his desk.