Although jailed in 1902, Piatnitsky managed to make his escape and he returned to Germany to continue his work as a courier for the "Iskra" group. He was a delegate to the 2nd Congress of the RSDLP in London in the Summer of 1903 — a gathering which split the RSDLP into rival Bolshevik and Menshevik wings. Piatnitsky sided with Lenin and the Bolsheviks at that gathering and he remained a loyal member of that faction throughout the pre-revolutionary years.