Investigators have been trickling into 10 Amistad St., the building where missing student Annie Le GRD ’13 was last seen, since about 10 a.m. this morning. Some of the investigation’s top officials just arrived — including the special agent in charge of the FBI in Connecticut, Kimberly Mertz, and the Yale Police Department’s top two officials, Chief James Perrotti and Assistant Chief Ronnell Higgins — and could be seen entering through a loading dock to the building’s basement, where the investigators’ search efforts have been concentrated in recent days.