NEW YORK (AP) – A young ex-brokerage assistant testified Tuesday that his boss ordered him to pass a secret tip to Martha Stewart that led the style maven to trigger her well-timed sale of ImClone Systems stock.

Douglas Faneuil, the government’s star witness in the case, said broker Peter Bacanovic ordered him to alert Stewart on Dec. 27, 2001, that the family of ImClone founder Sam Waksal was dumping its shares.

Faneuil said he told Bacanovic, who was on vacation in Florida, about a flurry of selling by the Waksals that morning. He said Bacanovic blurted out: “Oh my God, get Martha on the phone.”

Waksal later admitted that he had advance knowledge that the Food and Drug Administration was about to reject an ImClone drug application – a decision that sent the stock on a sharp decline.

Faneuil, who was manning Bacanovic’s desk at Merrill Lynch & Co. on Dec. 27, testified that he took calls before 10 a.m. from Waksal’s accountant and Waksal’s two daughters – all demanding that Faneuil sell their ImClone shares.

He said he spoke to Bacanovic, who left a message for Stewart and then ordered Faneuil to tell her of the Waksal sell-off when she called back. Faneuil said he asked his boss whether passing the tip would be appropriate.

“Of course. You must,” he said Bacanovic replied. “That’s the whole point.”

Stewart was unavailable and on her way to her own vacation in Mexico. But she called later in the day and ordered her entire stable of 3,928 shares of ImClone to be sold, the prosecution contends.

The government claims Stewart and Bacanovic cooked up a false story and repeatedly lied to investigators, saying they had a pre-existing arrangement to sell ImClone when it fell to $60 per share.

The testimony of Faneuil, a lanky 28-year-old who was soft-spoken in his answers on the stand, is the most critical piece of the puzzle that the government says implicates Stewart.

His testimony was delayed by five days after the judge penalized prosecutors for being too slow in turning over an FBI document that defense attorneys say raises questions about Faneuil’s credibility.

When court recessed Tuesday, Faneuil had not reached the point in his testimony where he was expected to say he actually told Stewart the Waksals were selling. While Faneuil testified in general terms about improperly passing information from one client to another, details of his exchange with Stewart are expected to come out Wednesday morning.

Lawyers for Bacanovic and Stewart are carefully planning a strategy for Faneuil’s cross-examination, which could begin as early as Wednesday. Faneuil had initially supported Bacanovic and Stewart’s story, but changed his story in a 2002 plea deal with prosecutors.

The defense is expected to argue that Faneuil was willing to lie to the government to get out of prosecution for his involvement in the ImClone sale.

Prosecutors sought to blunt that argument as soon as Faneuil took the stand Tuesday. Prosecutor Karen Patton Seymour asked him whether he had ever committed a crime.

“I told one client about what another client was doing in his account,” Faneuil said, “and then lied about it to cover it up.”

Defense lawyers are also hoping the judge will allow them to question Faneuil about past drug use, and Bacanovic’s attorney has suggested he will argue Faneuil himself decided – without Bacanovic’s approval – to tip Stewart.

Faneuil also testified that Stewart was one of Bacanovic’s two most-valuable clients and was close enough to her that he got some shares in Stewart’s own company when it went public.

Faneuil was steady in his answers to prosecutor Karen Patton Seymour. He praised his ex-boss.

“Peter was the best boss I ever had,” Faneuil said. “It was a great working relationship. He was demanding yet appreciative.” He said he socialized with Bacanovic, but did not consider him a friend.

Earlier Tuesday, a defense attorney moved to raise doubts about Faneuil by getting a former supervisor to admit she once reprimanded him for cursing on company e-mail.

Judy Monaghan, an administrator at Merrill Lynch & Co., also testified she told Faneuil to stop using company e-mail for personal messages.

Monaghan gave no details about the content of the e-mails.

Stewart faces five counts carrying a potential prison term of 30 years. Bacanovic faces five years carrying 25 years. Both would likely get lighter sentences under federal guidelines if convicted.