PORTLAND – Two years later, the question remains unanswered: Why did Mohamed Atta and Abdulaziz Alomari come to Portland to launch the nation’s worst terrorist attack?

The two men drove a rental car from Boston to stay at a hotel in South Portland on the night before the attacks. On Sept. 11, 2001, they barely caught their commuter flight back to Boston’s Logan International Airport, where they just made their connection with the jet they later would crash into the World Trade Center.

“We are still working every day to try to figure out the exact reason why they came up here,” said James Osterrieder, special agent in charge of FBI operations in Maine. “We are doing things throughout the world to make those determinations and answer those questions.”

Local authorities said the terrorists probably wanted to split up the team, so that all of the hijackers would not be arriving at the same airport. That way they would draw less attention, and if some were intercepted, others could continue.

The theory may be sound, but the FBI can’t accept it as true until it’s proved.

“If they were here to communicate with somebody, that’s obviously extremely important for us to find out, and we will continue to do everything we can to answer those questions,” Osterrieder said.

Suggestions that Atta and Alomari departed from Portland International Jetport to avoid security at Logan ignores the fact that the pair still had to pass security in Boston when they moved from one terminal to the other to make their connection.

The FBI has explored almost every theory, Osterrieder said. Maybe Atta wanted to be separate from the main group to direct the operation from a distance. Maybe, some people say, they wanted to submit to fate and if they succeeded in flying to Boston from Portland, the mission was endorsed by God.

In the days right after the attack, and still today, Maine’s 10 FBI agents have tried to confirm why the two chose to fly through Portland. “We just don’t want to not answer that question. It may have died with them and we may have to admit that at some point. We’re not at that point,” he said.

After publicizing information about the movements of Atta and Alomari in Maine and releasing photographs taken from security cameras at and near the jetport, the FBI sought tips from anyone who may have seen the pair.

“We had hoped that if they went anywhere other than the places we were able to find … we wanted to make sure they came forward and told us that,” Osterrieder said. “We didn’t want to have any gaps.”

Right after the attacks, the Maine-based agents received 2,200 telephone tips, 600 of which deserved follow-up investigation. The agents now spend about half of their time working on terrorism investigations.

“We’re getting information in volumes from jurisdictions around the world, and we piece that together as it relates to Maine,” Osterrieder said.

Osterrieder said there is urgency to chasing down leads.

“I do not want to be going back out to the airport the day after an incident occurs like we did last time,” he said. “We want to be trying to uncover a future event, before it happens, or uncover someone who may be assisting a terrorist cell that may be residing in Maine or may be providing financial support or logistical support.”