In an effort to identify two people who may be connected to the mysterious death of a top British codebreaker, authorities have published images of a man and woman who entered his apartment building weeks before his death.

Gareth Williams, 31, was found dead and naked in a North Face duffel bag in the bathtub of his flat last August. The sports bag was padlocked on the outside.

The two, said to be in their 20s and of Mediterranean appearance, were let in to Williams' building by another tenant in late June or July. They told the tenant they had keys to Williams' flat but indicated they knew him as Pier Paolo.

Williams, described by those who knew him as a "math genius," worked for the U.K.'s Government Communications Headquarters (GCHQ) helping to break coded Taliban communications, among other things. He was just completing a year-long stint with MI6, Britain's secret intelligence service, when he died. The flat where he lived was part of a network of flats registered to an offshore front company and rented out to GCHQ workers.

Williams had been dead for at least a week when his body was found. His mobile phone and a number of SIM cards were laid out on a table near the body, according to news reports. There were no signs of forced entry to the apartment and no signs of a struggle. The keys to the padlock on the duffel bag were found inside the bag beneath Williams' body.

The codebreaker reportedly had made repeated visits to the United States to meet with the National Security Agency and worked closely with British and U.S. spy agencies to intercept and examine communications that passed between an al Qaeda official in Pakistan and three men who were convicted last year of plotting to bomb transcontinental flights.

Investigators haven't ruled out the possibility that Williams was killed over something related to his work but believe his death may have been related to his personal life. Investigators believe Pier Paolo was an alias Williams may have used that was borrowed from Pier Paolo Pasolini, a controversial Italian filmmaker who made films that included sexual violence. According to recent reports, Williams had accessed five bondage websites prior to his death.

Williams flew up to four times a year to the United States to the NSA's headquarters at Fort Meade, according to the British paper the Mirror. His uncle, Michael Hughes, told the paper that Williams would mysteriously disappear for three or four weeks.

"The trips were very hush-hush," Hughes said. "They were so secret that I only recently found out about them – and we're a very close family. It had become part of his job in the past few years. His last trip out there was a few weeks ago, but he was regularly back and forth."

Williams was said to have worked with the NSA on e-mails intercepted between Abdullah Ahmed Ali and Assad Sarwar and Rashid Rauf, a British national in Pakistan who was allegedly director of European operations for al Qaeda. The e-mails, intercepted by the NSA in 2006, allegedly contained coded messages.

The NSA shared the e-mails with British prosecutors but wouldn't allow them to use the evidence in an early trial of the suspects out of fear of tipping off Rauf that he was under surveillance. It was only after Rauf was reportedly killed in a U.S. drone attack that the NSA allowed prosecutors to use the e-mails to convict the other suspects.

It's never been known whether the NSA intercepted the messages overseas or siphoned them as they passed through internet nodes on U.S. soil as part of the NSA's controversial and unconstitutional warrantless wiretapping program.

An unidentified Western intelligence source told the Mirror that Williams' job would have had him participating in "crucial high-level meetings with American intelligence officers. His job would have been crucial to the security of the U.K. and our interests abroad – and also to America and Europe. Although not particularly high up the GCHQ ladder, the importance of his role should not be underestimated. The man was a mathematical genius."

His landlady, Jenny Elliott, told the Telegraph, "Occasionally, you could hear tapes whirring from his flat, which must have been audio cassettes he used for work, but he never told me what they were."