A former Robinson Secondary School student disappeared last weekend, just two days before he was to appear as a key trial witness against two other former Fairfax County high school students accused of distributing massive quantities of LSD, according to law enforcement officials.

On Sunday, U.S. Park Police found a car and clothing belonging to Seth Michael Ferranti, 20, on the banks of the Potomac River near Great Falls.

The police also found a suicide note in the car and an empty vodka bottle on the ground, said sources close to the investigation.

Sgt. Peter Gentile, of the park police, said police are investigating whether Ferranti, who faced a minimum of 20 years in prison on a drug charge, jumped into the water.

So far, he said, police have found no evidence of a body.

"The area's been searched by boat, air and foot," Gentile said.

"We don't know for sure whether anybody went in."

Law enforcement officials said they are attempting to determine whether Ferranti staged a suicide hoax to avoid appearing at this week's drug trial of Aaron Taylor, 23, a former Lake Braddock High School student, and Chris Buckley, 20, who once attended Robinson.

That trial, in U.S. District Court in Alexandria, began yesterday and is expected to bring several former and current Fairfax high school students to the witness stand.

People familiar with the case said Ferranti was a critical witness, having kept written records of hundreds of drug transactions. They said it was unclear what impact his absence would have on the case.

Taylor and Buckley, two of six former Lake Braddock and Robinson students indicted in the case in September, have been charged with conspiring with a Burke-based drug organization that sold more than 100,000 doses of LSD during the last school year alone, much of it to juveniles who still attend Robinson.

The ring is also accused of selling several pounds of marijuana at Northern Virginia high schools and state colleges.

The other four defendants have pleaded guilty and agreed to testify against their former friends in hopes of reducing their sentences.

Ferranti entered into a similar agreement with prosecutors last summer, pleading guilty to running a drug distribution network and agreeing to help the government to prosecute his former assistants, including Buckley.

Assistant U.S. Attorney Christine Wright, the lead prosecutor in the case, said during her opening arguments yesterday that Buckley was one of Ferranti's closest friends.

"Mr. Buckley was Seth's right hand man, his best friend -- and an individual who could move pounds and pounds of marijuana," she said.

Thomas C. Carter, an attorney for Ferranti, said his client "never gave us any indication that he was going to do anything but cooperate."

Carter said Ferranti's parents are distraught, but added, "They don't think he would have committed suicide."

The government has described Ferranti's drug organization as one that began with a small group of friends, most of whom met in high school, who went from personal use of LSD to massive sales with the help of a West Coast drug contact made by Taylor.

Christopher Miller, who has pleaded guilty in the case, said he was told that with Taylor's contact, "the sky was the limit -- that as much as you wanted he could get it."

Miller, a Robinson graduate who went on to Radford University near Roanoke, also told the jury that when Ferranti took a Hawaiian vacation last June, he was put in charge of the group's LSD sales, while Buckley took over the marijuana business.

William B. Moffitt, Taylor's attorney, assailed the government witnesses during his opening remarks, reminding the jury that most of them were testifying as a way to reduce their prison time.

"These are young middle-class children who are confronted with this choice: Name names or face up to 20 years mandatory minimum terms without the prospect of parole," Moffitt said.

John Karr, a lawyer representing Buckley, said his client actively resisted getting involved in drug sales.

"Ferranti was after Chris Buckley for at least two years to join up and make some easy money," Karr said. ". . .Chris Buckley said, 'No, I won't do it.' "