NEW YORK – The arrest of a former hedge fund portfolio manager in a lucrative insider-trading scheme indicates authorities may be setting their sights higher, on a wealthy business leader connected to the suspect’s firm, an expert says.

Mathew Martoma made an arrangement to obtain secret, advance results of tests on an experimental Alzheimer’s drug that netted more than $276 million for his fund and others, according to charges filed in U.S. District Court in Manhattan.

He was arrested Tuesday on allegations that he used the information to advise other investment professionals to buy shares in the companies developing the drug, then later to dump those investments and place financial bets against the companies when the tests returned disappointing results.

Martoma’s trades helped reap a hefty profit from 2006 through July 2008, while he worked for CR Intrinsic Investors LLC of Stamford, Conn. CR Intrinsic is an affiliate of SAC Capital Advisors, a firm owned by Steven A. Cohen, one of the nation’s wealthiest hedge fund managers.

The government has been scrutinizing SAC since at least November 2010, when the FBI subpoenaed SAC and other influential hedge funds. Martoma is the fourth person associated with SAC Capital to be arrested on insider-trading charges in the past four years.

Martoma will have great incentive to cooperate with the government because the size of the gains would add years, if not decades, to any potential sentence upon conviction, said John Sylvia, co-chairman of the securities litigation practice at the Mintz Levin law firm in Boston.

It was clear from the court papers that Cohen was referenced frequently and was a likely target of investigators, he said, though they might not be able to build a sufficient case against him.

“There’s little doubt as to where the government’s sights are,” Sylvia said. “I don’t think it takes Sherlock Holmes to figure it out.”

Martoma was arrested at his home in Boca Raton, Fla., and made an initial appearance Wednesday in federal court in West Palm Beach, Fla. He was released on $5 million bail on charges of conspiracy to commit securities fraud and securities fraud, and was told to return to court Monday in Manhattan.

Martoma’s attorney, Charles Stillman, called his client “an exceptional portfolio manager” who expects to be exonerated.

SAC spokesman Jonathan Gasthalter said the company and Cohen “are confident that they have acted appropriately, and will continue to cooperate with the government’s inquiry.”

The Securities and Exchange Commission filed civil papers in the case against CR Intrinsic Investors, Martoma and Dr. Sidney Gilman. The civil complaint said the illegal money was earned in July 2008, when various hedge funds traded ahead of a negative public announcement involving the clinical trial results of an Alzheimer’s drug being developed by pharmaceutical companies Elan Corp. and Wyeth.

The SEC complaint said Martoma carried out the scheme with Gilman, an 80-year-old professor of neurology at the University of Michigan Medical School who served as chairman of a safety committee overseeing the clinical trial.

U.S. Attorney Preet Bharara said Martoma gained from “cultivating and corrupting” Gilman, eventually receiving $9 million in bonus pay for the year when the trades were made. Martoma met with the doctor about 42 times, beginning in the summer of 2006, and eventually convinced him to start talking about the drug trial, prosecutors said.