Harvard sent out alerts about "a report of a man with a gun in the area of Smith Campus Center" - formerly the Holyoke Center - in the heart of Harvard Square around 3:30 p.m. The alert was called off not long after - after Cambridge Police found and arrested the man.
The initial alert from Harvard read:
Shelter in place. If outside go inside a Harvard building. If in a building stay where you are.
Cambridge Police reported:
A suspect reportedly lifted his shirt and displayed a gun in his waistband to 2 men; was described as wearing a red, white and blue vest over a white hooded sweatshirt; black rimmed glasses.
At 3:53 p.m., Harvard rescinded the stay-in-place directive:
The individual has been apprehended and is in custody. The shelter in place is lifted.
H/t Tony Corsentino, Yawp and Emma.