An armed man opened fire during a company board meeting inside a commercial building at the Navy Yard last night, killing three men and critically wounding a fourth before turning the gun on himself.

Police said the shootings occurred about 8:30 p.m. during a meeting of the board of directors of a company called Watson International. The board was meeting at 5131 S. 11th St. in a structure known as Building 79, a former Navy procurement office that, like many of the warehouse-type buildings at the former Navy base and shipyard, is now home to private businesses.

At the scene last night, Deputy Police Commissioner Richard Ross said the gunman opened fire with a semiautomatic pistol during a regularly scheduled meeting on the second floor. Police believe the gunman was a participant in the meeting, Ross said.

Police did not disclose the relationship between the shooter and the victims, but said the shootings happened after a dispute broke out during the meeting.

"It appeared that the shooter was upset over something that was going on inside the business," Ross said.

The cause "appeared to be something concerning money," Ross said.

The scene inside the conference room was "utter chaos," he said.

Police said they think Watson is an investment company.

Two other people were in the building when the shootings occurred. The gunman bound both with duct tape but left them alone. They were being interviewed by homicide detectives last night. Ross said one had been so tightly bound that police had to cut him free.

When police arrived, they exchanged gunfire with the shooter inside the building as he stood about 100 yards away at an office door. He then went behind the door, and police were not sure if they had hit him, Ross said.

Officers at the scene called for SWAT support. At that point, someone from inside the building came from behind the shooter and told police that he was dead. Police said the fatal wound was self-inflicted.

"This is a tragic situation," Ross said, "one that you always hope would not hit Philadelphia. Unfortunately, today it did."

The names of the dead men were not released.

The wounded man, whose name also was not released, arrived at Thomas Jefferson University Hospital about 9 p.m. with multiple wounds. A spokesperson said the man underwent surgery but remained in critical condition.

About 10:30, a woman leaped out of a police vehicle and was hustled into Jefferson's emergency-room entrance at 10th and Sansom Streets.

Building 79's primary occupant is Zigzag Net Inc., a Web site development company involved in advertising. It was unclear last night what the relationship was between Zigzag and Watson International, but officials indicated that they might have been business partners.

John Grady, senior of vice president of Philadelphia Industrial Development Corp., which is in charge of leasing space at the Navy Yard, said Building 79 is a 10,000-square-foot, two-story building on the waterfront. About a year ago, Zigzag leased 5,000 square feet on the second floor. The shootings occurred inside Zigzag's space.

Contributing to this report were Inquirer staff writers Robert Moran, Michael Klein, Henry J. Holcomb and Daniel Rubin.