He intended to target post offices, police cars and soldiers returning from abroad.
Police put together a video of what Pimentel is accused of trying to pull off.
Investigators say he tried to make a pipe bomb following instructions from a well-known al-Qaeda publication.
New York City officials say Pimentel is an al-Qaeda sympathizer and a follower of Anwar al-Awlaki, the radical American-born cleric who was killed back in September.
Mayor Michael Bloomberg says this is the 14th terrorist plot to target the city since 9-11.
None has succeeded.