Mark David Norris, who was killed Monday in the boardroom of his Navy Yard marketing company, was an entrepreneur who projected a stylish image and the sense that he had an inside line on the next big business trend.

"He was a talented designer, a real great business person," said David Brown, president of Brown Partners MultiCultural Marketing. "Mark has always been such a level-headed guy. I can't imagine him being involved in this."

Others say there were clues that Norris, 46, of Pilesgrove, N.J., the president and chief executive of Zigzag Net Inc., may have operated several businesses too close to the margins. Police say Norris, his brother and a business partner were killed by an investor who claimed they had defrauded him.

According to public records, state and federal tax agencies have filed liens against Zigzag for nearly $180,000 in back taxes and unemployment compensation.

And some who knew Norris said his business deals often seemed fragile.

"He always played very close to the edge," said John Serpentelli, 42, an animation artist who was Norris' romantic partner for seven years. "He was very charismatic and convincing."

Serpentelli said the tension caused by the business pressures contributed to their breakup in 1999. "It was just too much high stress and slippery slope," he said. "He always believed in the next thing to come along.

"He was always wheeling, dealing," Serpentelli, who lived with Norris in West Philadelphia, said yesterday.

Police said Vincent J. Dortch, 44, of Newark, Del., gunned down Norris and his brother Robert E. Norris, and their business partner James M. Reif Jr., over allegations that they had misspent his investment on an Upstate New York conference center they were rebuilding.

The eldest of four brothers, Mark Norris went to school at the U.S. Merchant Marine Academy in Kings Point, N.Y. He dropped out in his freshman year, early in 1979, and enlisted in the Marine Corps. He came to Philadelphia as a Marine recruiter. After his discharge, the self-taught artist began producing and selling paintings to galleries, Serpentelli said. From the art world, he migrated into marketing.

Ambitious and outgoing, Norris achieved business success by recognizing early the power of the Internet. He fashioned his marketing business to incorporate contemporary Web designs.

"The man was talented," said Mark Segal, publisher of the Philadelphia Gay News, who met Norris after the artist fashioned a new logo for Philadelphia International Airport, where Segal is on the board of directors.

Though he acknowledged to friends that he was gay, Norris did not trumpet his orientation because he said it could be bad for business, Serpentelli said.

Two years ago, Norris and another man moved into a two-story stucco house in the Thoroughbred Homes development in Pilesgrove, a village in Salem County.

Norris founded Zigzag in 1997 in South Philadelphia and moved the company into new offices in the Navy Yard two years ago. In a 2004 interview in the Philadelphia Tribune, he said his company had annual billings of $2.5 million.

Last year, the company won a Philly Gold Award for best public service advertising campaign for its "Tough Choices" Web site to encourage at-risk African American youths and others make responsible choices about HIV-AIDS.

But a $236,000 HIV-AIDS campaign Norris designed last year for the Philadelphia Department of Public Health that equated high-risk sexual behavior to gun violence was criticized by gay, African American and AIDS activists, who called it insensitive. In response to the uproar, the city pulled the plug on the campaign.

Contributing to this article were Inquirer staff writers Mark Fazlollah, Jane M. Von Bergen and Jonathan Wilson.