Out of uniform, Amy DiVirgilio can easily be mistaken for a student walking in the Yard. The thin, 5-foot 5-inch 25-year-old with dangling earrings and brown hair pulled back in a ponytail appears to be just like any college student.

But that’s before she dons a bullet-proof vest and the uniform of the Harvard University Police Department (HUPD), and straps on her gun belt, filled with a baton, two-way radio, pepper spray, handcuffs and a nine millimeter Glock 22 handgun.

Then she climbs behind the wheel of an HUPD cruiser to begin her eight-hour shift keeping the campus safe. Each shift is different, and she never knows what any night will bring. Tonight, thankfully, is quiet.

7:19 p.m.—DiVirgilio obtains permission from the watch commander to leave her normal patrol zone around the Radcliffe Quad and patrol “all sectors.”

The 4 p.m.-midnight shift that DiVirgilio works is HUPD’s largest—and, often, its busiest.

Her nightly patrols take her from the Somerville line to the Charles River and beyond into the Business School campus in Allston. The land travelled is familiar territory to her.

She grew up just 15 miles from Harvard Square—although the journey from her home to Harvard has been a long and indirect one.

DiVirgilio says she never aspired to be a police officer—she says she was not assertive enough growing up to be one. However, she has always wanted to help people.

“I was always trying to assist someone else, even if it meant my life would be turned upside down,” says DiVirgilio, who, as a teenager, used to buy 15 Big Macs from McDonald’s and distribute them to homeless people in Harvard Square.

As a college senior, DiVirgilio was majoring in economics and planning a career in international business—until she realized that she was on a path to spend the rest of her life in an office building.

Instead, after graduation, she decided to enlist in the Marines. Six months after that, instead of entering flight school and committing herself to eight-and-a-half-years with the Marines, DiVirgilio returned home.

“I was thinking, ‘What if I want to get married? Will I drag my husband from base to base?’ And I knew I couldn’t have children and fly,” she recounts.

When she found that HUPD was hiring, she decided to apply.

After obtaining a position with HUPD, DiVirgilio attended the state police academy in Quincy, Mass.

“I had fun. I’d go back any day if I got paid for it,” she says. “Not that I enjoy ironing. That was the worst part.”