Two cops arrested three men – one with a loaded revolver – during a “vertical patrol” in the Bronx Wednesday night, according to police sources.

The officers, Francis Conejo and Paul Velez, were walking down the stairs in an apartment building on Morris Avenue in Fordham Heights at about 8:50 p.m. when they spotted two men, one carrying a loaded .357 Rossi USA gun, on a second-floor landing, the sources said.

Marquis Southwell, 20, tried to run before the pair of cops took him down to the ground and grabbed his gun. Southwell, of the Bronx, whose gun was defaced, was placed in federal custody. He was hit with multiple weapon and trespass charges, and has 22 prior arrests. Nathaniel Rodriguez, 28, of the Bronx, who was with Southwell on the landing, was also charged with trespass, the sources said.

The officers later spotted Shaw Karron, 16, on the stairwell looking up to the second floor. Karron, also of the Bronx, who told police that he knew Southwell and Rodriguez, was charged with trespass and unlawful possession of marijuana.

The incident comes as NYPD vertical patrols have fallen under heightened scrutiny.

Officer Peter Liang, the rookie cop who accidentally shot and killed the unarmed 28-year-old Akai Gurley during a vertical patrol in the stairwell of a Brooklyn housing project in Nov. 2014, was convicted of manslaughter on Thursday.

And last week, two officers, Diara Cruz and Patrick Espeut, were shot and wounded while on routine vertical patrol at a Bronx housing project.