New York's finest returned to the scene of the alleged crime just a few minutes ago -- combing Amanda Bynes' apartment building for information and witness statements.
Law enforcement sources tell us ... NYPD cops got statements from the night doorman as well as 2 other employees, who were there when Amanda was allegedly smoking marijuana in the lobby and acting crazy.
We're told cops also went upstairs to Amanda's floor for more witness statements.
As we reported ... cops arrested Amanda after finding weed in her apartment. They also say she threw a bong out the window, allegedly to 86 evidence of a crime.
Amanda was charged with weed possession, attempted evidence tampering and reckless endangerment.