Allen said he was a casual member of the group in the late 1980s and early 1990s. He said he did purchase books the National Alliance published and would sometimes provide legal advice to the organization but that he hasn't been a member in more that a decade.
"Whether you believe me or not, I'm not a member of the National Alliance, haven't been for many years," Allen said. "You cannot find a single person who can say, 'Glen Allen' treated me disrespectfully."
He said of his past affiliation with the group: "I will acknowledge emphatically that that was a huge mistake."
He said he had a number of experiences in the Army that shaped his worldview, and he then became curious about the group.
But then, he said, "I disagreed with them on several things, and I just stopped giving them money."
Heidi Beirich, the center's intelligence project director, wrote in a post Wednesday on the center's website that "Allen's history with organized racism and anti-Semitism is deep."
The Southern Poverty Law Center said it obtained records showing Allen was a dues-paying member of the National Alliance for years.
"Allen was also a subscriber to the NA's racist publications, purchased entrance to a Holocaust denial conference the group held and bought a Holocaust denial DVD the group sold," Beirich wrote in her post.
City Council President Bernard C. "Jack" Young said the Rawlings-Blake administration was right to terminate Allen's contract.
"I am angry that someone who allegedly harbors such disgusting views as Mr. Allen was allowed to work on behalf of the citizens of Baltimore," Young said in a statement. "I am pleased that Mr. Allen's contract with the City of Baltimore has been terminated. Moving forward, each department and city agency should conduct an internal review of their hiring practices."
The mayor's office said in a statement that Allen retired from "a large and respected law firm" in January and began working for the city on a one-year contract in February.
"Mr. Allen was fully vetted at the time of his hire — and of course had decades earlier been professionally and character tested upon his admission to the bar," the statement said. "None of the historical facts and alleged facts recently publicized about Mr. Allen's political views and affiliations were disclosed or discussed when his contract was agreed to. The law department does not as a general practice question its hired or contract attorneys about their political views."
Allen was helping to defend the city in a lawsuit brought by an African-American man who alleges that police officers withheld and fabricated evidence to convict him wrongfully of murder.
Sabein Burgess was sentenced in 1995 to life in prison in the shooting death of his girlfriend, Michelle Dyson, in her Harwood home the year before.
The Mid-Atlantic Innocence Project began raising doubts about Burgess' involvement in 2010, and a Baltimore judge ordered a new trial in 2014. Then-State's Attorney Gregg L. Bernstein dropped all charges against Burgess, and he was freed after 19 years in prison.
Burgess filed his lawsuit against the mayor, City Council, Police Department and several officers last year.
McCarthy said Allen was working as support staff on that case and no others. McCarthy said his removal will not affect the litigation.
The action against Allen comes a week after the U.S. Department of Justice accused the Baltimore Police Department of a pattern or practice of discriminatory policing and civil rights violations.
In a report, Justice Department investigators said police practices in Baltimore "perpetuate and fuel a multitude of issues rooted in poverty and race, focusing law enforcement actions on low-income, minority communities" and encourage officers to have "unnecessary, adversarial interactions with community members."
The Justice Department began investigating the department after the death last year of Freddie Gray. Gray, 25, died after suffering a severe spinal cord injury in police custody.
City Solicitor George Nilson said Allen played "absolutely no role" in the law department's assessment of the Gray case, the Justice Department investigation or "any alleged police brutality lawsuits — zero." McCarthy said the mayor "had no involvement whatsoever in [Allen's] recruitment and hiring."
Allen said he believed a disgruntled member of the alliance provided old records to the Southern Poverty Law Center that named him.
He was aware that he was being investigated by the center, he said. Once the report appeared online, he expected to be fired from the city. He said the report exaggerated any connection he once had to the alliance.
"They throw these things up there like I'm a huge contributor," he said. "I'm just getting slapped around because I crossed some lines the Southern Poverty Law Center draws."
He said he "wanted to do something to help the city. I'm not a Baltimorean, but I actually had become fond of the city and I wanted to make a contribution."
Now, he said, "I'm damaged goods."
At DLA Piper, he worked in a wide range of areas, including securities fraud, contract disputes and defamation, according to the firm's website.
Officials with DLA Piper did not respond to requests for comment.
Allen holds a degree from the University of Maryland School of Law and clerked for former Maryland Court of Appeals Chief Judge Robert Murphy.
Breaking News Alerts Newsletter
As it happens
Get updates on the coronavirus pandemic and other news as it happens with our free breaking news email alerts.
According to his website, Allen lived on a Zuni Indian Reservation as a young child, is married with three children, has written novellas and poetry and has won gold medals in the 400 meter run at the Maryland Senior Olympics.
City Councilman Brandon Scott, vice chairman of the council's public safety committee, said Allen's hiring reflects poorly on the city.
"Before we hire anybody in this day and age we should be doing thorough checks," Scott said. "I'm disgusted. It's unacceptable."
Baltimore Sun reporters Tim Prudente and Ian Duncan contributed to this article.