Police say the sex attack happened during the afternoon on Wednesday, June 22.
Police say the man lured a 12-year-old into Simcha Hall, a Borough Park synagogue located at 50th Street and 15th Avenue.
Once in the basement, police say the man, dressed in tradition Hasidic attire, sexually assaulted the boy.
About an hour later, a second boy, 11, was confronted by the same man in front of the synagogue.
Police say that boy was not sexually assaulted but was lured into the synagogue.
The Special Victims Crime Unit is now handling the case as they search for the suspect.