For weeks, prosecutors were on a roll. Guilty pleas accumulated in the college admissions bribery scandal: the mastermind, former athletic coaches, a test-taking expert and more than a dozen wealthy parents, including a Hollywood actress. In all, 19 defendants admitted to conspiring to subvert the admissions process and more were preparing to do so.

But the first sentence blunted the prosecution’s momentum.

When U.S. District Senior Judge Rya W. Zobel sentenced former Stanford University sailing coach John Vandemoer on Wednesday to one day in prison, with the time deemed already served, she delivered a setback to prosecutors who wanted to put him behind bars for more than a year.

“It’s a sign perhaps for prosecutors to slow down,” said Daniel S. Medwed, a Northeastern University law professor. “Being very aggressive in sentencing recommendations might not always be in the best interest of justice. Some of these defendants are far more culpable than others.”

During the hearing in a Boston courthouse, Zobel had lengthy exchanges with Assistant U.S. Attorney Eric Rosen. She peppered Rosen with questions about the prosecution’s arguments regarding fraud and bribery and the facts underlying the racketeering conspiracy that Vandemoer had acknowledged with a guilty plea in March.

Prosecutors said Vandemoer agreed to accept $610,000 in bribes to help prospective students get into Stanford as sailing recruits. But the judge said she was convinced that Vandemoer was less culpable than others charged in the scandal because he had not pocketed bribes for personal gain. Instead, the money went to the Stanford sailing program. Zobel imposed a $10,000 fine and two years of supervised release, including six months of home confinement. Vandemoer, 41, avoided prison. He apologized in court and noted that his career is gone. “I deserve all this,” he said. “I caused it.”

Analysts say the sentence sent a message that the Varsity Blues case unfolding in federal court is best understood as a series of cases with unique circumstances. The allegations, they say, do not necessarily add up to one vast conspiracy, but a cluster of smaller conspiracies.

Each involves a scheming consultant named William “Rick” Singer, who has admitted to breaking the law. Singer sought to help the children of wealthy parents get into prominent universities through cheating on admission tests and the use of fake athletic credentials to pose as recruits for sports such as sailing, rowing, soccer and water polo. Thirty-three parents are accused of funding bribes to perpetrate the fraud. Some paid hundreds of thousands of dollars to help their children get into schools including Yale and Georgetown universities and the University of Southern California.

Stanford expelled one student associated with Singer who was not a sailing recruit. Others Vandemoer assisted in the scheme were not admitted to Stanford and wound up at other universities.

Zobel is scheduled to sentence Singer in September. He has pleaded guilty to racketeering conspiracy, money-laundering conspiracy, conspiracy to defraud the United States and obstruction of justice. Singer is cooperating with investigators in an effort to obtain leniency. But if Zobel’s comments were any indication, he could face significant punishment. The judge noted in court that transcripts of phone calls show Singer heavily pressured Vandemoer into breaking the law.

Several judges are assigned to the Varsity Blues cases, which makes it especially difficult to predict how Wednesday’s development will influence other outcomes. Legal experts said they believe some accused parents face a significant risk of prison time.

Thirteen parents, including actress Felicity Huffman, have pleaded guilty to fraud conspiracy and a 14th has agreed to do so. Nineteen, including actress Lori Loughlin and her husband, Mossimo Giannulli, have pleaded not guilty to fraud conspiracy and money-laundering conspiracy. Facts vary significantly in those cases and others involving Singer’s alleged accomplices.

Huffman, for example, acknowledged paying $15,000 to help her older daughter obtain a fraudulent SAT score. She awaits sentencing in September, with prosecutors recommending at least four months in prison.

Loughlin and Giannulli are contesting allegations that they paid $500,000 to help their daughters get into USC as purported rowing recruits. They appear headed to trial. That could deepen their prison jeopardy if convicted.

“You can’t judge all of these cases the same,” said Ellen Podgor, a Stetson University law professor who analyzes white-collar crime. “You have to look at the individual as well as the circumstances. You’ve had a lot of pleas so far. Some of them may get higher sentences even though they may be pleading and cooperating. In some cases, you’ll get the prison time, and in some cases you won’t.”

On Wednesday, Rosen urged Zobel to send Vandemoer to prison to “set the tone for these cases going forward.” He depicted the first sentence as a watershed moment for the largest college admissions scam the federal government has ever prosecuted.

“That message is simple, but it does need to be said: If you pay or receive bribes, if you lie and cheat, and if you engage in a scheme that ultimately results in the theft of a college admissions spot from someone who deserves it, you will be criminally prosecuted and you will be sent to prison,” Rosen said.

After Zobel issued the sentence, the U.S. attorney for Massachusetts, Andrew E. Lelling, pledged to press forward.

“Mr. Vandemoer agreed to accept $610,000 in exchange for corrupting the admissions process of a major university,” Lelling said in a statement. “We will continue to seek meaningful penalties in these cases.”

Lelling’s office declined further comment Thursday.

Vandemoer’s sentence drew scorn and sarcasm from many quarters.

“Well that sends a strong message to the ruling class,” Kevin Carey, an education policy expert with the think tank New America, wrote on Twitter.

Others cautioned not to read too much into it.

“Vandemoer isn’t a great barometer for other defendants in the case & what their sentences might be,” Chris Villani, a courts reporter for the news site Law 360, wrote on Twitter. “Here, the government struggled to identify a ‘gain’ or ‘victim’ in the court’s opinion, since no students were admitted and he didn’t pocket any money himself.”

Weintraub reported from Boston.