It is currently well established that globular clusters (GC) host multiple stellar populations, as evidenced from the split evolutionary sequences in their colour-magnitude diagrams and from the large internal variations in elements affected by proton capture (e.g., C, N,O, Na, Mg, and Al). In this scenario, a fraction of the first generation stars, which activated in their interiors hydrogen burning via the CNO cycle, have furnished the ashes from which the second-generation stars have been formed. However, while the general picture of different stellar generations co-existing in each GC is quite well assessed, one fundamental question is as yet unanswered: which were those polluters? In this talk I will present our results, focusing on light (Li and F) and heavy elements (synthesised through neutron-capture process), in a large sample of stars in several clusters: these abundance determinations bring us a key tool to investigate the nature of the stellar polluters in globular clusters and provide us with a strong observational constraint to theoretical models.