Paul's lawyer, Richard Wolson, was livid after learning Thursday of the online allegations.
"Alex Paul has, from the beginning, said he has absolutely nothing to do with the death of his wife, whom he loved. These are scandalous, injurious, untruthful remarks," Wolson told the Free Press.
"They are slanderous and libelous. And they are meant to hurt, meant to scandalize."
Wolson said they will be reviewing the website in more detail before deciding what action to take.
RCMP are continuing to investigate the high-profile March 13 shooting death of Diane Paul and have not named any suspects.
Alex Paul was arrested days after reporting his wife dead but then released 24 hours later without charges. He recently submitted to a police polygraph test -- against his own lawyer's advice -- following pressure from his wife's family including Tomkins.
Tomkins, his brother Derek and cousin Tarrie Ficzycz also took the lie detector test and passed, according to RCMP.
Paul's results have not been made public by police.
Tomkins told the Free Press on Thursday he's posted the content on the website, which had previously been used as a tool for keeping Dauphin residents updated about what was happening in their community.
"I own the domain. I'm probably going to be getting a call from his lawyer, aren't I?" he asked.
Tomkins admitted he is trying to put pressure on his stepfather, the police and the community to ensure his mother's case is solved quickly.
There are three pages on the website. The first simply contains large blue text stating "Murder of a beautiful woman... Diane Gloria Ficzycz."
The second page contains most of the content that the mayor says is false and defamatory: "On March 13, 2007, Diane Gloria Ficzycz (Paul) was murdered! No longer are there suspects, but one suspect! A breach of trust, a loss of love, a coward, a murderer took the life of a beautiful mother and baba! The suspect is the murderer! How can you live with yourself!? Four polygraphs were taken. Three passed -- Robbie Tomkins, Derek Tomkins and Tarrie Ficzycz. All passed and are considered witnesses by the authorities. The fourth did not pass!!! He failed it completely!!! The murderer failed!!!"
There is no information included in the web page that indicates the basis of the allegation that anyone failed a lie detector test.
Wolson told the Free Press his client recently took a second polygraph test through a private company and passed. The results have been forwarded to police, he said.
The third page on the website shows a large, candid photo of Alex Paul with the words "Justice Will Be Served" beneath.
There has been a clear divide in the family since Diane Paul was killed.
Paul has only spoken publicly on two occasions. The first was at his wife's funeral, after Tomkins urged him to step forward and say a few words. The second was during a recent city council meeting in which he thanked citizens -- in a letter read aloud by the deputy mayor -- for their support and vowed to continue serving them.
"This has been the most difficult time of my life. Diane and I were always together and I don't know how I am going to get over this," Paul wrote.
RCMP returned to the scene of the crime last month in an attempt to find the missing gun they believe was used to kill Diane Paul.
Police spent several hours searching the fields around the victim's home, located on the edge of Riding Mountain National Park.
Police have also established a toll-free "tipline" asking for people to contact them with any information about the case.