Police have arrested a suspect in the murder of a 47-year-old man who was shot to death by two masked men at an apartment in Washington Heights just before the holidays, cops said Friday. The masked duo fatally shot David Brown after he let them into an apartment in the Polo Grounds Towers NYCHA building on Frederick Douglass Blvd. near W. 155th St. about 10:55 p.m. on Dec. 14, according to police. Police responding to a 911 call discovered Brown with a gunshot wound to the abdomen. Medics rushed him to Harlem Hospital but he could not be saved. Cops arrested Daniel Spencer, 47, in Manhattan at around 9:30 a.m. Thursday. Spencer, who lives in East Harlem, is charged with murder, criminal weapons possession and criminal use of a firearm, according to police. Police are still searching for the second suspect.