Can a cocker spaniel dog really be a successful drug-sniffing dog...?

...I was watching the MSNBC Lockup documentary series, and they had a show on world prisons. In one Polish prison, a commentator says she was expecting to see a German Shepherd or Rottweiler to sniff for contraband...weapons and drugs...which is normally used in American prisons. She said it was like watching a Disney movie when a cocker spaniel was used for the job and found the contraband.