An ongoing argument over money between two friends led to the fatal shooting of a 19-year-old at the Savin Hill T station, prosecutors said yesterday.

Nhu Nguyen, 19, of Dorchester, and Derek Matulina were friends until they began arguing when Nguyen believed Matulina owed him from a drug transaction, authorities said.

The two crossed paths by chance May 7 at the T stop and Matulina hit Nguyen in the head with a padlock tied to a handkerchief. That’s when Nguyen shot him in the chest, authorities said.

He was ordered held on $100,000 cash bail after pleading not guilty during his arraignment in superior court.