Authorities say it does not appear the suspect, who was seen on surveillance video, and the victim knew each other.
In the first robbery June 29, police say the suspect followed Brandon, sneaked up behind him and snatched the chain off his neck.
Eleven days later, authorities say the suspect followed Brandon to his home in Long Island City, forced his way into the apartment, grabbed him by the throat and threw him to the floor, causing him to lose consciousness.
The suspect then stole electronics from the home and ran off.
Brandon says he still feels weak from the attacks.