According to published reports, the man has followed his victims into their apartment buildings... once in an elevator on East 12th Street and Third Avenue. Then per DNAinfo:
He followed a 28-year-old man into an apartment building at 381 East 10th St. about 5:25 p.m. on Jan. 19, threatened him with a knife and demanded his messenger bag, police said, but the victim refused to hand over the bag and the suspect ran off.
The media reports on the robberies did not include a physical description of the suspect.
Anyone with information that could help in the investigation is asked to call Crime Stoppers at 1-800-577-TIPS (8477). You may also submit tips online.