Boston police arrested a Boston University medical student yesterday in the slaying of a New York woman at a luxury Back Bay hotel last week and an earlier attack on another woman. Both victims had advertised personal services on Craigslist.

After an intensive manhunt along the Eastern Seaboard, Philip Markoff, 22, of Quincy, was stopped by police around 4 p.m. while driving south on Interstate 95 in Walpole, Boston Police Commissioner Edward Davis said at a press conference last night at police headquarters.

The second-year medical student was charged with fatally shooting 26-year-old Julissa Brisman April 14 at the Marriott Copley Hotel and with the armed robbery and kidnapping of a prostitute who was tied up at the Westin Copley in the Back Bay on April 10.

Brisman had advertised her masseuse service on Craigslist; the second victim was a prostitute who advertised through the online classified website.

"We are very, very happy to have this man off the streets in a timely way," Davis said.

The arrest was made in two crimes whose brazen nature and swanky locale shocked Boston residents, drew national attention, and exposed the seamy world of prostitution fostered by the anonymity of the Internet. Police in Warwick, R.I., would not comment last night on whether Markoff is a suspect in a similar attack that occurred in a hotel there Thursday.

Suffolk District Attorney Daniel F. Conley called Markoff "a predator" who may have attacked other women he met through similar Craigslist ads.

"There may be other victims out there with a similar MO, a Craigslist MO, and if there are, we want to help you," Conley said at the news conference.

Authorities arrested Markoff following what Davis called a round-the-clock investigation that relied on forensic evidence including fingerprints, electronic evidence, and photographs of the suspect taken by hotel surveillance cameras.

Federal and state investigators and police from Massachusetts and Rhode Island "followed high-tech leads and used old-fashioned shoe leather," Conley said.

Ellen Berlin, chief spokeswoman for the Boston University School of Medicine, said Markoff has been suspended because of the criminal charges.

He is one of more than 600 medical students on the school's South End campus and was featured grinning broadly in a 2007 Globe photograph as he showed off his white medical coat with other students at the school's annual White Coat Day ceremony.

One medical school colleague recalled meeting Markoff at orientation and studying anatomy with him. She said, "He seemed like a nice guy, and he was a helpful, smart kid."

Markoff is engaged to be married and attended the State University of New York at Albany before entering medical school, according to two law enforcement officials.