10 days ago, at twilight, four teenagers approached someone affiliated with Harvard near Peabody Terrace, pushed him to the ground and stole his wallet. The police response was swift. Units from the Cambridge Police Department (CPD) and the Harvard University Police Department (HUPD) canvassed the area, but couldn't find the robbers.

The next day, HUPD issued its thirteenth community advisory, warning the University of yet another threat.

The advisories are becoming nearly commonplace this fall, as violent crime against Harvard affiliates has risen.

The trend has police searching for answers, and has concerned students and college administrators.

A significant detail of the trend, though, is its randomness.

The pattern is that there is no pattern: four undergraduates assaulted by alleged skinheads, another two assaulted by persons unknown, two affiliates indecently assaulted, one sexually assaulted, four street robberies on Harvard's campus, and a serious unprovoked assault on a runner on the bike path near the River.

Bike theft is up. Larcenies from motor vehicles are up.

While last year, HUPD's first community advisory was issued in mid-October to warn about the Yard Burglar, HUPD has already issued 13 this fall.

Partly, HUPD Chief Francis D. "Bud" Riley says that is because the police are issuing them for more types of crime this year.

"We've been told that the community advisories are useful to people," Riley says. "Issues that might have been a judgement crime last year, we're now putting out advisories for."

But there has been a distinct increase in the number of students victimized this year

As far as police can tell, there is no single reason for the larger number of attacks. The descriptions of the incidents have varied widely. HUPD and CPD crime analysts have been unable to piece together any pattern, investigators say.

The modus operandi of the attacks have varied--daylight, early evening, nighttime--as have the descriptions of the suspects--white, black, single, pack, old, young. Some crimes have been committed on foot, others on bicycle and even others in vehicles.

Since no pattern has emerged, it has made the life of HUPD's and CPD's detectives difficult.

"If we had more arrests and fewer suspects, we'd have a better idea why," said HUPD spokesperson and crime analyst Peggy A. McNamara.

But perhaps the simplest answer for the crime increase is Harvard's urban location. Crime is up throughout Cambridge--by four percent so far this year.

Robberies--armed and unarmed--are up seven percent this year.

(Police say this is not necessarily a cause for concern; last year's total was the lowest in 25 years).

Nonetheless, students often forget what lies at their doorstep.

Right outside Harvard's gates, the Pit in Harvard Square is one of Cambridge's hotbeds of criminal activity. Each weekend brings HUPD and CPD calls to the Pit and Au Bon Pain. So much so, in fact, that on Friday and Saturday night, HUPD stations an officer there.

According to CPD's police reports, in the past three years, the Pit has been the site of nine aggravated assaults, three simple assaults, two street robberies, ten drug arrests, one disorderly conduct arrest, one drinking in public arrest, three pickpocketings and one weapons violation arrest--and that does not count crimes reported to HUPD or the MBTA Police.

Just in the year alone, CPD records show there have been 12 calls for intoxicated people, eight disturbance calls, seven fight calls, one gang call, one overdose and 11 suspicious person calls in the Pit.

But while students often have not been vigilant on campus safety in the past--the success of the Yard Burglar last fall in Matthews Hall depended on unlocked doors--HUPD says a watchful campus has helped their efforts this fall.

Police say more students and staff members are reporting suspicious people. This has led to several arrests this fall--increasing arrest totals but potentially preventing future crimes. And as HUPD emphasizes, all crime is local.

"We're concerned about every crime that occurs around here," Riley says.