As the trial of a former Brooklyn judge whose courtroom was awash in bribes began yesterday, prosecutors described a corrupt relationship between the jurist and a veteran attorney who regularly appeared before him.

For the Brooklyn district attorney, Charles Hynes, the trial of the former judge, Gerald Garson, is a watershed in Mr. Hynes’s investigation into the Brooklyn judiciary. The investigation, which involves allegations that judgeships in Brooklyn could be bought by the highest bidder, began in earnest four years ago with the arrest of Judge Garson on bribery charges. At that time, according to news reports, Judge Garson pledged his services to aid prosecutors in proving that judgeships were in fact sold. More than four years later, Mr. Hynes has yet to bring forward any charges alleging that is the case, although prosecutors say the investigation continues.

In state Supreme Court in Brooklyn yesterday, no traces were on display of those reported days of cooperation between Judge Garson and prosecutors. Prosecutors accused Judge Garson of deciding cases while he was a judge in matrimonial court not according to the law or the facts, but according to the wishes of an attorney who was his dinner partner.

“He ran that courtroom and he ran it corruptly,” an assistant district attorney, Joseph Alexis, said to jurors of Judge Garson. “And he ran it by whim.”

The lawyer who allegedly held a great deal of influence over Judge Garson, Paul Siminovsky, spent more than $12,000 taking the judge out to restaurants and bars between 2000 and 2003, Mr. Alexis said.

A portion of the prosecution’s evidence comes from a video camera installed by investigators in Judge Garson’s robing room. Prosecutors have already played some of that footage — including video of Mr. Siminovsky handing the judge $1,000 in $100 bills — in an earlier trial involving allegations that a court officer and law clerk steered cases toward Judge Garson.

In other proceedings, prosecutors have proved that litigants who appeared before Judge Garson paid bribes in an attempt to influence their cases, but it is not yet established whether Judge Garson was aware of these illegal payments.

The defense attorney, Michael Washor, argued that widespread rumors among litigants in divorce proceedings that Judge Garson could be bought were traceable to Mr. Siminovsky. The lawyer, Mr. Washor said, “was wheeling and dealing and committing fraud on his own clients.”

Judge Garson was above involvement in such criminal activity, Mr. Washor said.

“They ate and they drank and they were friends,” Mr. Washor, said of the relationship between the lawyer and Judge Garson. “Siminovsky knew Gerry would eat and drink with anybody, but when he put on his robe and got on the bench he was a judge who would” give justice equally.

Still, Mr. Washor conceded that Judge Garson did not “act in the way you would expect a judge to act.”

The fine line separating criminal acts from lesser, inappropriate judicial conduct will be closely scrutinized throughout the case. Indeed, two courts had dismissed the bulk of the charges against Judge Garson on the grounds that the alleged misdeeds were suited to review by a judicial disciplinary body, not criminal court. The state’s highest court reinstated the charges.