His first stop is the athletic complex across the river. He walks from building to building, testing doors to make sure they are locked. One door swings wide open.

"This is a good thing I'm finding it before someone else does," Gilbert says.

He radios the dispatcher that he'll be conducting a search inside. But after looking in bathrooms, locker rooms, cinder-block hallways, and coaches' offices, he finds no one inside.

Back on the streets, most of his patrol will be spent watching sidewalks and alleys through the window.

While Gilbert is alone for much of his patrol, even on the graveyard shift he gets to know students. Undergraduates sit on the porches of Matthews and Weld Halls past 4 a.m. Later, as the sun rises over Boston Harbor, he'll offer escorts to varsity athletes headed to the Murr Center and nearby fields.

"I try to interact as much as possible," he says. "We're here for the students. We're here for the protection of the school."

Tonight, as the clock in the Square shows 2 a.m., a herd of tow trucks descends on Mass. Ave. The city sweeps the streets early in the morning, and anyone who has left their car out overnight faces a tow and a $100 fine. The tow trucks whoosh down the street like giant insects, pausing only briefly to grab a car before vanishing into the night.

2:48 a.m.--Gilbert parks outside Byerly Hall and heads into Radcliffe Yard. He's hoping to find the man who lurked around Byerly yesterday. But Gilbert has his priorities: before walking around the yard, he studies the sprinklers, trying to figure out which ones will go on next.

On quiet nights like tonight, two of his most potent enemies are sprinklers and roving skunks. One night, with the windows down, a sprinkler hit him squarely in the chest and face.

A skunk would be worse.

"You gotta keep your flashlight on, because you never know where you're going to find a skunk," he says.

2:59 a.m.-- Boston Herald workers fill paper boxes and toss freshly printed newspapers onto the sidewalk for newsstands. In another hour or so, the Globe will arrive; The Crimson hits the Square around 6 a.m.

3:03 a.m.--A motion alarm sounds across the river in Allston. Gilbert and his backup, Officer Terence Johns, race towards the site. Their blue strobes light up the darkened businesses, freezing them in the bright lights; the engine roars as Gilbert pilots his way across the river, screeching to a stop at the building within two minutes. He sees two Harvard employees just walking out as he pulls up. It takes 10 minutes to search the building--nothing is amiss.

"They probably just didn't make it out in time after setting the alarm," Gilbert says. But he'll return to the site later in the night. He eventually decides that the heating system was at fault.

Second Watch

The 8 a.m. to 4 p.m. shift is similar to that of any day job. Much larger than the midnight shift, HUPD's daytime officers watch over Harvard offices and students as they head to class.