Acting on a tip, the Cambridge Police Department last week arrested a homeless man, charging that he raped a city woman last Monday.

Louis Bruno, 20, was arraigned late last week, and is now in a Middlesex County jail cell.

Police said that Bruno first spotted the young woman, whom he did not know, in Harvard Square around noon Monday morning.

Later that day, he followed her as she walked toward Central Square. At the corner of Pearl and Magazine streets, he grabbed her from behind, dragged her into a nearby building, and raped her, police said.

The woman, who was not affiliated with Harvard University, gave police a detailed description of the man who attacked her--including the type and style of clothes he wore.

A citizen, who police would not identify, called detectives on Wednesday to report that a man matching the suspect's description was seen loitering around the same intersection the rape occurred last Wednesday.

CPD detective John Poirier and a patrol sergeant, Joseph McSweeny, quickly drove to the area.

When they arrived, they saw Bruno, and "had a short discussion with him," said CPD spokesperson Frank D. Pasquarello.

Bruno was then arrested.

Last Monday's assault was the third "stranger rape" recorded in the city this year. There have been six incidences of "acquaintance rapes"--assaults where the victim knew the attacker.

According to Pasquarello, common sense can help protect the public from being vulnerable to assaults.

"Hopefully, anytime you're not familiar with an area where you live and work, try to walk with someone," Pasquarello said.

Pasquarello also advocated the use of personal protection devices like stun-guns and piercing whistles.

He urged women in particular to attend a self-defense course, which the CPD holds free of charge.

Because the woman first saw her attacker in Harvard Square, officers with the Harvard University Police Department (HUPD) assisted in the investigation and issued a community advisory last Wednesday. Officers were told to keep an eye out for the suspect.

The Crimson yesterday reported that the CPD had not arrested a subject, based on information available over the holiday break.

HUPD was not aware of the arrest until today, said Peggy A. McNamara, a HUPD spokesperson.

A CPD official contacted Sunday would not confirm to a reporter that a suspect had been arrested.