A former Bank of America broker, Theodore Sihpol III, was found not guilty of helping a New Jersey hedge fund illegally trade in mutual funds after the stock market had closed, a defeat for New York’s attorney general, Eliot Spitzer.

A jury of seven women and five men in Manhattan acquitted Mr.Sihpol, 37, of 29 counts of larceny, securities fraud, and falsifying business records following six days of deliberations. The jury deadlocked on four counts, leading New York State Supreme Court Justice James Yates to declare a partial mistrial.

The acquittal imperils three similar Spitzer prosecutions scheduled for trial in the fall. Mr. Sihpol’s trial was the first to arise from Mr. Spitzer’s investigation of mutual fund trading and may encourage other accused executives to go to trial rather than settle, as most have during a series of inquiries by his office into the financial industry over the past three years.

“Sihpol’s winning at least in some way dents the notion that Spitzer is unbeatable,” said Mark Winston, a partner at Baker & McKenzie in New York and a former federal prosecutor. “It could serve to embolden at least other individual defendants charged by Spitzer’s office.”

“The Sihpol case is one of eight cases where criminal charges were brought,” Spitzer spokesman Brad Maione said in a statement. “Six other individuals have pleaded guilty to fraud and related charges.”

He declined to comment on the four deadlocked counts.

Judge Yates scheduled a hearing for June 23, at which time Mr. Spitzer may have to decide whether to seek a new trial on the four counts. They include one count each of securities fraud and scheme to defraud, and two counts of falsifying business records.

“This acquittal is a blow to Eliot Spitzer, who has been unable to prose cute Wall Street criminals successfully,” said lawyer Jacob Zamansky, whose 2001 claim against Merrill Lynch & Company helped spark Mr. Spitzer’s investigation of biased Wall Street research. “By comparison, federal prosecutors have a strong record,” he said. “Spitzer should concentrate on working to prove his cases rather than trying people through the press.”

Mr. Spitzer contended in Mr. Sihpol’s case that buying or selling after hours, known as late trading, was a crime because it diluted the return of fund members who were not granted the same advantage.

Mr. Sihpol’s lawyers argued throughout the trial that late trading was legal and that their client never intended to commit a crime.

The jury “agreed with our view of the evidence that what Ted did was openly known” and not fraudulent, said one of Mr. Sihpol’s lawyers, Evan Stewart, a partner at Brown Raysman Millstein Felder & Steiner in New York. “There was no clear line in the sand that said this conduct was wrong.”

Three other people charged in Mr. Spitzer’s mutual fund investigation are currently scheduled to be tried before Judge Yates in September.

They include Grant Seeger, the former chief executive and founder of Security Trust, a Phoenix-based retirement plan administrator that Mr. Spitzer says helped Canary Capital Partners disguise late trades.

The other two defendants are William Kenyon, a former president of Security Trust, and Paul Flynn, former managing director, Canadian Imperial Bank of Commerce.

Mr. Flynn’s case also involves a hedge fund called Samaritan Asset Management. Security Trust has since been dissolved by banking regulators.

“I think the Attorney General’s Office will have to go back and really think about whether the prosecution of Seeger, Kenyon, and Flynn is worth their efforts,” said Mr. Kenyon’s lawyer, Henry Mazurek. “It’s the same set of facts and one jury has already rejected their prosecution theory. All Flynn did was help set up a line of credit at CIBC.”

Mr. Mazurek said he had been following Mr. Sihpol’s case closely. “I sort of expected this verdict given the nature of the charges and how the prosecution went about trying to label the broker as the criminal while the hedge fund was doing something they didn’t know was wrong,” said Mr. Mazurek.

Former SEC lawyer Ernest Badway said the case is only a “bump in the road” for Mr. Spitzer. “This is one area. Let’s not forget he’s gotten a number of settlements from major brokerage firms involving this mutual fund late trading,” said Mr. Badway, a lawyer in Newark, N.J.

Barbara Penn, the jury foreperson, called Mr. Sihpol a “scapegoat” and a “fall guy” during an interview outside the courthouse after the verdict was read. She said that most of the jurors were sympathetic toward Mr. Sihpol from the beginning of the trial.

“He had been punished enough,” said Ms. Penn, 56, a guidance counselor, who added that Mr. Sihpol had lost his job and that his reputation had been sullied as a result of the case. “The sympathy was there from the beginning for that.”