Marc S. Dreier knew the 45th-floor conference room of Solow Realty well. He had been in it many times as a trusted lawyer for the company’s founder.

So nothing seemed amiss when he showed up one afternoon in October and told a receptionist he had a meeting with her boss, people associated with Solow say.

Mr. Dreier was elegantly dressed, as always, the people said. He had three people with him. The receptionist ushered the group past her desk. They were sitting there, visible inside the glass-walled room, a few minutes later when the boss, Steven M. Cherniak, happened to walk by.

Mr. Cherniak would later tell people at the company how surprised he had been to see Mr. Dreier. He had not scheduled any meeting with him, and he had no idea what Mr. Dreier was up to.

But people there gave little thought to Mr. Dreier’s odd visit until November, when the company’s founder, Sheldon H. Solow, received a disturbing call. The caller wanted to let Mr. Solow know that Mr. Dreier had offered him the chance to buy promissory notes that had been issued by the company, people associated with the firm said.

Dec. 2, Mr. Dreier flew to Canada by private jet and tried to hold a meeting there very much like the unauthorized gathering he is said to have held in Solow’s Midtown Manhattan offices, the authorities say.

In the offices of the Ontario Teachers’ Pension Plan, the authorities say, he tried to pass himself off as a lawyer for the plan and close the sale of an additional $33 million in fraudulent promissory notes supposedly backed by the plan.

A receptionist there caught on, the authorities said, and called the police, who arrested him.

In the world of computer security, that’s known as social engineering. Hackers have recognized for a long time that it is far easier to trick someone into giving up their password than to "hack" it via wizardry.

Dreier was apparently so good at it that even where detected by the boss no one questioned what he was up to until they got an explicit warning of fraud.