A security guard employed by a Brooklyn-based company is dead after being shot while on the job in Westchester County. 

According to investigators, the victim's supervisor, identified as 32-year-old Dontan L. Jenkins, has been arrested and charged with second-degree murder in connection with the shooting. 

They say that Jenkins and 47-year-old Richard Brown, who is from the Bronx, both worked as unarmed security guards for Nature's Finest Security, which provides residential, corporate and celebrity security. A gun was recovered at the scene. 

Police believe the two men had some sort of argument Monday morning, which led Jenkins to return that evening and shoot Brown inside the booth where he worked at an apartment building in Mount Vernon. They say Brown had only been employed for 10 days. 

Nature's Finest Security said it cannot comment on the investigation, but offered thoughts and prayers to the victim's loved ones.