Cox left his job as an insurance agent to work as a mortgage broker for a local company. While there he developed a reputation for unscrupulousness, which was heightened by his authorship of an unpublished 317-page manuscript entitled The Associates. The novel’s protagonist, who shares many traits in common with Cox, travels the country committing mortgage fraud. Cox told co-workers about the book, and elaborated its details to them. “He sent it to a lot of people to see if they thought it worked” said a former co-worker. After being fired from the company when he was convicted of mortgage fraud in 2002, Cox faked a good credit history, and used that to buy dozens of homes and properties. In one instance he used the social security number of a toddler, and all of his documents—references, bank letters, rent receipts, W-2s from nonexistent employees—were counterfeit. He used his skills as an artist to decorate the properties with elaborate art deco-style murals. Several of his future girlfriends said that his painting talents were part of his allure, though the St. Petersburg Times described his works as copies of murals by Tamara de Lempicka. Cox charmed Alison Arnold, a young local married woman, into believing he could give her a wealthy and luxurious life. While courting Arnold she said he took her to crime films such as The Italian Job and Catch Me if You Can—which he reportedly adored and watched several times—and detailed his criminal plans to her.

Cox and Arnold grew apart and eventually Cox began courting another woman. Rebecca Hauck, a divorced mother of one, had moved to Tampa after falling into debt and declaring bankruptcy in Las Vegas. She had already committed criminal offenses before meeting Cox; Hauck was fired from a job in Las Vegas for forging her employer’s name on checks that she used to pay her debts. They met through an online dating service. She, unlike Arnold, was willing to leave her son. After finding out that Jeff Testerman, a reporter for the St. Petersburg Times, was investigating him, Cox and Hauck left town. Two days later, on December 14, 2003, the newspaper published Testerman’s story, “Dubious Housing Deals Line Avenue”.

Authorities in the Atlanta area discovered Cox’s activities, and eventually his identity. On August 6, 2004, the United States Secret Service issued arrest warrants for Cox, alleging conspiracy, identity theft, mail and wire fraud, money laundering, and social security number fraud. News broadcasts showed photos of Cox and Hauck and requested that viewers provide any information pertaining to their whereabouts. By spring 2005, the couple had eluded authorities for eighteen months, using dozens of identities, including ones stolen from former co-workers and acquaintances. Cox also stole identities from the homeless by posing as a survey–taking Red Cross worker to acquire their social security numbers. At this point, due to remorse and anxiety, Arnold called the FBI and confessed. She was sentenced to two years in prison for numerous offenses, including conspiracy to commit bank fraud and identity theft. Arnold was also ordered to pay $300,000 in restitution to her victims. Shortly thereafter, Cox filed multiple mortgages on two houses for $886,318 in Columbia, South Carolina in less than a week. An abstractor noticed this, and a fraud alert was issued on one of Cox’s money-laundering bank accounts. He was arrested when he returned to the bank to make a transaction, but he told authorities his name was “Gary Lee Sullivan”, one of about thirty aliases Cox had at the time; because “Sullivan” had no open warrants, the police released him. Shortly afterwards, Cox and Hauck moved to Houston, but they separated and she remained there in hiding under an assumed name. A year later the Secret Service found Hauck and arrested her. Convicted on numerous counts, Hauck was sentenced to six years in prison, and five years of supervised release. In May 2006, after being on the run from authorities for two and a half years, Cox was placed on the Secret Service’s Most Wanted Fugitives List.

Estimates of the amount of money Cox fraudulently obtained range from $5 million to more than $15 million, to more than $25 million. He is believed to have fraudulently mortgaged more than 100 properties. Cox was serving a 26-year sentence at the Federal Correctional Institution (FCI), a low-security facility in Coleman, Florida. He was ordered to pay $5.97 million in restitution, and testify against his co-conspirators. As of 2010, the United States Attorney’s office has not brought charges against any of his 13 Tampa-area cohorts, even though Assistant U.S. Attorney Robert A. Mosakowski informed a judge in 2005 that he planned to bring charges against up to 13 accomplices.

The week that Hauck was sentenced to prison, Cox was living in Nashville, Tennessee under the name Joseph Carter. He was dating a single mother, Amanda Gardner, who was unaware of his criminal past, and posing as the owner of a home restoration business. He told her he was from a wealthy family, and his silver 2005 Infiniti and “fashionably decorated bungalow” seemed to confirm this. Cox used a falsified passport to travel to Europe on a cruise of the Greek Isles with Gardner. He did not spend much time in Italy or Greece due to his intense fear of Interpol. Gardner’s 60-year-old babysitter, Patsy Taylor, suspected something about “Carter” didn’t add up. When she found out he was originally from Florida, she researched him online and eventually discovered that the man she knew as “Joseph Carter” was really Matthew Cox. Fearing for the safety of Gardner’s son, Taylor reached out to Jeff Testerman of the St. Petersburg Times, who had closely followed Cox for more than three years. Testerman in turn put Taylor in touch with Rebecca Hauck’s lawyer. Hauck’s family paid Taylor for Cox’s address, as this information could be used to reduce Hauck’s sentence. He temporarily escaped capture due to a chance series of events. Cox and Gardner’s home was burglarized, and they checked into a hotel. On November 16, 2006, Cox was arrested by a half dozen Secret Service agents—who had been pursuing him for more than two years—when he and Gardner returned from the hotel. He had been building Williamson a house using his fake identity and credit history, but, fortunately for his friend, he was arrested before Williamson could give him a down payment. Hauck’s sentence was later reduced from 70 to 42 months as a result of her assistance in Cox’s capture.

Cox faced 42 counts of fraud, in addition to felony charges for fleeing while on probation from a previous conviction. Facing a maximum sentence of over 400 years, he negotiated a plea bargain agreement that gave him a maximum of 54 years, and a $2 million fine. On April 10, 2007; Cox formally pleaded guilty to six counts of bank fraud, identity theft, passport fraud, conspiracy to commit mortgage fraud, and violating the terms of his probation from his 2002 mortgage fraud conviction. On November 17, 2007, federal judge Timothy C. Batten, Sr. sentenced Cox to 26 years in prison. He also ordered Cox to pay $5.97 million in restitution.

While in prison, Cox mailed several letters to the St. Petersburg Times in 2008 in which he accused politician Kevin White of taking bribes from him during Cox’s criminal career. He claims he made payoffs to White, an ultimately successful candidate for the Tampa City Council, in 2002 and 2003. Cox said White told him he could not receive the money directly, and suggested that Cox have friends donate $500 each, and then reimburse them. Records and statements from those who donated show that Cox did in fact make numerous contributions to White’s campaign, and reimbursed others who did so as well. White, he claims, agreed to vote to rezone vacant properties in Tampa and Ybor City. When Cox was first arrested, the FBI talked to him about White, whom they were also investigating, and he told them the same information. He claimed to have paid him $7,000 in cash in addition to the recorded contributions he arranged. When White and a fellow City Council member were told Cox’s contributions might have been illegal in 2004, his colleague told the police, while White kept silent. White has denied that he knew these contributions were reimbursed, and called Cox’s accusations “the jailhouse ramblings of a reputed con man.” White said he befriended Cox when he came to believe the con man was interested in revitalizing Tampa Heights. Cox had fled the Tampa area before White cast any rezoning votes, so there is no voting record which could help confirm the validity of his accusations. In 2012, White, who had gone on to serve as Hillsborough County Commissioner, was convicted of unrelated federal bribery and corruption charges and sentenced to three years in federal prison.