Commissioner Ed Davis said Monday that Phil Markoff was arrested after being stopped in south of Boston on Interstate 95 in Walpole.
Davis says authorities had the Boston University student under surveillance "for days" before arresting him.
Markoff is charged with killing Julissa Brisman, 29, who was found dead Tuesday at the Boston Marriott Copley Place. Police say the New York City woman advertised massage services on Craigslist and had a massage table set up in the room where she was shot.
Markoff is scheduled to be arraigned in Boston Municipal Court on Tuesday.
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