BOSTON , Massachusetts -LRB- CNN -RRB- -- Friends and acquaintances of Philip Markoff , a medical student accused of killing a woman he may have met through a Craigslist online ad , described the 23-year-old as a model student . Medical student Philip Markoff , 23 , appears in court Tuesday in Boston , Massachusetts . `` My girlfriend actually rode the elevator with him a lot alone ; it 's kind of freaking her out now , '' said Patrick Sullivan , who lived in the same apartment building as Markoff in Quincy , Massachusetts , a Boston suburb . `` She thought he was kind of the all-American , good-looking guy , '' Sullivan said . `` When she saw him on TV yesterday , she even remarked , ' I ca n't believe it 's him . I always thought he had such a great smile , and he was so nice to me . ' '' James Kehoe , a friend of Markoff 's from the State University of New York at Albany , where both attended college , said Markoff was `` one of the best students I 've probably ever encountered . '' `` He would never put anything in front of his work , '' he said . `` He had great aspirations to be a doctor . '' Markoff , a second-year student at Boston University 's School of Medicine , is charged with killing 26-year-old Julissa Brisman of New York on April 14 at Boston 's Copley Marriott Hotel . Watch acquaintances describe a smart , good-looking guy '' Markoff was arraigned Tuesday and is being held without bail . His attorney , John Salsberg , told reporters after the hearing that Markoff is `` not guilty of the charges . He has his family 's support . I have not received any document or report or piece of evidence other than what I heard in the courtroom . All I have at the moment are words -- no proof of anything . '' A Boston University spokeswoman said the school suspended Markoff , who has no criminal record , when it learned of the charges on Monday . `` This was a brutal , vicious crime . Savage , '' Suffolk County District Attorney Daniel Conley told reporters . `` And it shows that Philip Markoff is a man who 's willing to take advantage of women -- to hurt them , to beat them , to rob them . '' A procedural not-guilty plea was entered on Markoff 's behalf , Conley said . Evidence from the scene suggests that Brisman `` put up a fight , '' prosecutor Jennifer Hickman said during the hearing Tuesday . Police have said that Brisman , a model , advertised as a masseuse on Craigslist , a popular online classifieds service . She suffered blunt head trauma , Hickman said , and was shot three times at close range . One of the bullets passed through her heart , killing her , she said . Markoff is also charged in connection with the April 10 robbery of a woman at a Westin Hotel in Boston . In that case , the woman made arrangements to meet a man through Craigslist for a massage at the hotel , but was held at gunpoint and bound , Hickman said . She was robbed of $ 800 and personal items and left tied to a door handle with duct tape over her mouth , the prosecutor said in court Tuesday . The victim was not identified . Megan McAllister , who identified herself as Markoff 's fiancee , maintained his innocence in an e-mail sent to ABC News . McAllister said Markoff `` is the wrong man '' and `` was set up . '' `` Unfortunately , you were given wrong information as was the public , '' she wrote . `` All I have to say to you is Philip is a beautiful person inside and out and could not hurt a fly ! '' She accused Boston police of `` trying to make big bucks by selling this false story to the TV stations . What else is new ?? '' Authorities believe the motive in Brisman 's death was robbery , Conley told reporters . In executing a search warrant at Markoff 's home , police found a firearm , along with restraints and duct tape , he said . Surveillance videos from the hotel where Brisman was killed showed a tall , clean-cut young blond man in a black windbreaker leaving the property , according to Boston police , who had sought public assistance in identifying the man . Police traced the Internet communications with Brisman to an e-mail account that had been opened the day before her death , Conley said . Using Internet provider information , they found the computer was at Markoff 's residence in Quincy . Authorities put the home under surveillance , Conley said , and `` the case just begins to build from there . '' Markoff , meanwhile , is `` bearing up , '' Salsberg said . `` It 's obviously a difficult time for anybody in these circumstances with the charges that have been brought against him . ... He 's pleaded not guilty . He is not guilty . '' Authorities in Boston are working with police in Warwick , Rhode Island , on what could be a related case . On April 16 at a Holiday Inn Express in Warwick , a man tied up and demanded money from a 26-year-old dancer who had posted a Craigslist advertisement , Warwick Police Chief Col. Stephen McCartney said . The robbery was interrupted when the woman 's husband entered the room . After pointing his gun at the husband , the suspect fled , McCartney said . He said the incident `` may be related to similar crimes occurring in the Boston area , '' but that had not been determined . Craigslist CEO Jim Buckmaster told CNN the company is `` horrified and deeply saddened that our community services have been associated in any way whatsoever with a crime of violence . '' He promised that Craigslist will evaluate the incident to see whether additional measures could be introduced to protect users . CNN 's Mary Snow and Randi Kaye contributed to this report .