Why so many Sheriff's cars at TAB building?

[zmgmeister.livejournal.com]

Went by the Tufts admin building ( old junior high between Broadway and Holland ) and there must have been at least seven county sheriff's cars parked on the Broadway side.

This usually means details for something that crosses city lines. Is there a parade or road race today? It could be related to Tufts graduation but that's not until Sunday.