During his last visit to the casino on April 16, Markoff applied for a credit limit. Approval from the casino was pending when he was arrested Tuesday during a traffic stop while he was en route to Foxwoods with McAllister, the source and law enforcement officials told ABC News.
"Markoff was the gambler, she didn't really play the tables,'' said the source. McAllister did not have an account at the casino.
"He always played blackjack and used black chips. He was not a high roller. But he liked to buy in for $100 or $500,'' the source said
Markoff is also being looked at in a third attack, this one also a robbery, in a Rhode Island Holiday Inn Express where, again, a woman was tied up after placing an advertisement on Craigslist for massage services.
A search of his Quincy, Mass., apartment, prosecutors said, turned up a semi-automatic weapon along with ammunition, plastic zip ties and duct tape.
But as sure as police are that they have the right man, his fiancee told ABC News Monday that Markoff was not the person responsible for the robberies and Brisman's murder.
"Unfortunately, you were given wrong information as was the public," Megan McAllister wrote to ABC News in an e-mail. "All I have to say to you is Philip is a beautiful person inside and out and could not hurt a fly! A police officer in Boston (or many) is trying to make big bucks by selling this false story to the TV stations. What else is new?? Philip is an intelligent man who is just trying to live his life so if you could leave us alone we would greatly appreciate it. We expect to marry in August and share and wonderful, meaningful life together."
Conley said there is "very powerful evidence" that Markoff is the man on the surveillance videos and that Leffler has identified him as the man who attacked her.
Conley said it's understandable that his fiancee would want to support her loved one, but that they wouldn't charge him with such a heinous crime unless they were sure.
Even though Markoff doesn't seem to fit the profile of a typical killer -- he's a clean-cut medical student who was engaged to be married this summer -- looks can be deceiving.
Michael Welner, a forensic psychiatrist and chairman of the Forensic Panel, told "Good Morning America" today that a good education has nothing to do with a person's character.
"So much of crime is about choices," he said. "This is a situation of someone who had everything to lose," and his choices imploded his life.
Welner said Markoff may very well have gotten in over his head during Brisman's alleged murder, "and I think more evidence is going to shed light on that."
He pointed out that the alleged crimes were about money, not sex or power.
Markoff opened an account at the Foxwoods casino in 2008, but his visits to the casino increased "in March and April," leading the Cheryl, N.Y., native to apply for a credit line in early April, a source with knowledge of the investigation said.
"He went to Foxwoods frequently, including visits on April 2, 12 and 16,'' the source told ABC News. "On the 16th he left with $5,300 in winnings.''
Markoff also used his hometown New York address at 803 Cheryl Road and the Quincy, Mass., apartment he shared with his fiancee to apply for a credit line. The highest single bet Markoff made was $1,000, the source said.
"He came once in 2008, but then he was here all the time starting in March,'' the source said.