Enlarge Pool photo by Mark Garfinkel Boston University medical student Philip Markoff, 23, is ordered jailed without bail by a Boston municipal judge Tuesday. Police say a Boston University medical student accused of robbing women who advertised erotic services on Craigslist, killing one of them, had items belonging to both victims in his apartment. A law enforcement official who spoke on the condition of anonymity told the Associated Press Wednesday that police found items belonging to both women in Markoff's apartment in Quincy, south of Boston. The source was not authorized to speak about evidence. READ: Commonwealth v. Markoff The source would not confirm a report by ABC News that the items seized by police included the victims' underwear. ABC News said two unidentified law enforcement sources said Markoff appeared to be collecting underwear as "souvenirs" from his alleged victims. Investigators are also looking into gambling as the possible motivation for the 23-year-old who was arrested on Monday on Interstate 95 in Massachusetts as he and his fiancee drove to Foxwoods Resort Casino. The Connecticut casino has confirmed it is cooperating with authorities investigating Philip Markoff's gambling habits. "We do not release information publicly concerning individual patrons; however, we are aware of this situation and are cooperating with the appropriate law enforcement authorities," the casino and its owner, the Mashantucket Pequot Tribal Nation, said in a statement. Suffolk District Attorney Daniel Conley refused to comment directly on reports that Markoff might have been seeking money to pay gambling debts. "As we explore various motives for the robberies, gambling is certainly a motive that we will look at," he said. Police in Boston and Warwick, R.I., say Markoff may have preyed on other women he found on the website, where people can post most ads for free, says Jake Wark, a spokesman for the district attorney in Suffolk County, Mass., who brought the charges. A judge ordered Markoff jailed without bail. Markoff will next court appearance was set for May 21. He is charged with murdering one woman and robbing and kidnapping another. Both had posted ads under the website's "erotic services" section, police say. Craigslist CEO Jim Buckmaster, in a statement posted on his blog Tuesday, urged website users to take "the same common-sense precautions online as they would offline," such as choosing a public place or bringing a friend along when meeting people encountered online. About 50 million Americans use Craigslist to place online classified ads each month, he wrote. "We are horrified and deeply saddened that our community services have been associated in any way whatsoever with a crime of violence," he wrote. "We are evaluating this incident closely to see if there are any additional things (Craigslist) could be doing to further improve safety for our uses and the general public." Defense attorney John Salsberg said Markoff is not guilty and "has his family's support." "There are a lot of people out there, and not all of them are good," says Parry Aftab, a privacy and security lawyer who founded wiredsafety.org to promote online safety, including on popular sites such as Craigslist, Facebook and MySpace. "Many of us are vulnerable because we're not as careful in the online world as we would normally be." This is not the first time someone allegedly has used Craigslist to find a victim. Michael John Anderson, 20, of Savage, Minn., was sentenced this month to life in prison for killing Katherine Ann Olson, 24, whom he lured to his home when she responded to an ad for a nanny he put on the site. Craigslist signed an agreement Nov. 6 with 40 state attorneys general in which it promised to enact safeguards to restrict prostitution postings on its site. It requires people who post in the erotic ads section, which includes such services as fantasy role-playing and lap dances, to provide valid identification and pay a $5 or $10 fee by credit card. Despite that agreement, Cook County, Ill., Sheriff Thomas Dart last month sued Craigslist for facilitating prostitution. The suit, filed in Chicago, asks a judge to outlaw the "erotic services" section. Dart said in the lawsuit that his department had made hundreds of arrests based on ads on the site, including for child endangerment and human trafficking. Markoff is accused of contacting a 29-year-old woman who advertised massage services in the erotic services section of Craigslist, Wark says. He arranged to meet her April 10 at the Westin Copley Place hotel in Boston, Wark says. Once in her hotel room, Wark says, he pointed a gun at her, bound her hands and demanded money. Markoff is charged in that case with armed robbery and kidnapping. Markoff replied to another Craigslist ad April 14 and made an appointment to meet Julissa Brisman, 26, of New York, at the Boston Marriott Copley Place, Wark says. Brisman was beaten and shot three times at close range, he says. One bullet struck her heart, killing her. Markoff is charged with murder and carrying a firearm without a license. "The evidence suggests an armed robbery that escalated to violence," Wark says. He says police traced an Internet address used to set up the date with Brisman to Markoff's apartment in Quincy, Mass. Police also are investigating whether Markoff is linked to a similar armed robbery in Warwick, R.I., Wark says. Contributing: The Associated Press Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more