The federal corruption trial of state Probation Department officials wrapped up today where it began: With US District Court Judge William Young emphasizing to jurors that political patronage may be unseemly, but it isn’t illegal.

Patronage involves getting a job or promotion “based on who you know rather than what you know,” said Young in his jury instructions. “Patronage, standing alone, is not a crime.”

The government charges that former state Probation commissioner John O’Brien and two deputies, Elizabeth Tavares and William Burke III, directed a rigged hiring process at the Probation Department in which jobs were given to candidates sponsored by Beacon Hill lawmakers. The former Probation officials are facing mail fraud, racketeering, and racketeering conspiracy charges that could carry sentences of up to 20 years in prison.

For two hours Young held forth Tuesday morning, standing the entire time and likening his jury instructions to a “law school class pertaining to this case.”

He told jurors they are free to believe or question as they see fit any piece of evidence or the testimony of any witness. If they choose not to believe someone’s testimony, Young said, “It’s as if the witness never testified.” He urged them to apply “special scrutiny” to anyone who testified under a grant of immunity.

Young walked jurors up to the line separating illegal acts from those that are legal, even if sometimes questionable or inappropriate.

“Whatever you may think of it, it’s not a crime,” Young said of patronage hiring. He said it is “perfectly acceptable” for those in government to recommend someone for a job in government. He also said it’s not wrong for an office to keep records listing who has recommended whom for jobs, saying there could be “lots of innocuous reasons” to do so that don’t extend to criminal acts.

He said other actions might be deemed “questionable,” but still don’t rise to the level of crimes. Probation hiring involved a scoring system in which candidates were rated by interviewers. Young said letting those who rate the candidates know that a particular applicant was recommended by a government official might be questionable, but it still doesn’t constitute a crime.

Prosecutors allege, however, that the bogus hiring scheme O’Brien oversaw crossed those lines into criminal territory by utilizing a rigged scoring system for rating job candidates that violated the merit-based hiring procedures set forth in the Probation Department’s own hiring manual.

Young laid out the four elements the government must prove for a guilty finding on mail fraud charges, which lie at the heart of the prosecutors’ case:

1. That there was a “scheme or artifice” to defraud through false and fraudulent representations. The government says this was the rigged hiring scheme, in which scores were fudged to favor politically-connected candidates.

2. That the individuals charged in the case knowingly participated in the scheme. Young cautioned that hiring officials have a fair amount of leeway in favoring a well-connected candidate. If a candidate was legitimately in the pool of qualified finalists for a job but then selected for “the wrong reason” based on political connections, not merit, he said, that doesn’t cross the line into knowingly taking part in a fraudulent scheme.

3. That others relied on the materially false information, and money or property was provided that individuals would not otherwise have received. The reliance element centers largely on the actions of Robert Mulligan, who was the chief justice of administration and management for the state’s Trial Court. Young said Mulligan had to sign off on hiring decisions that O’Brien certified were the result of following the Probation Department’s written hiring policies. Mulligan has to have been duped by the alleged sham hiring process for this element to be proven. Young said in court on Monday, with the jury not present, that if Mulligan “knew what was going on there was no fraud because there was no material misrepresentation.” The “money or property” allegation centers on the jobs that prosecutors say lawmakers were essentially able to dole out as favors to politically-connected allies.

4. That the US postal system was used to help advance the scheme. This is essential for the charge of mail fraud to be proven. The government says some candidates applied for jobs by mail, while rejection letters were sent by US mail from the Probation Department to those passed over in the bogus hiring scheme.

Tavares and Burke were subordinates of O’Brien’s in the alleged scheme, and charges against them, Young told the jury, are only to be considered if they first find O’Brien guilty on one or more counts.

The racketeering charges, he instructed the jury, require the government to prove that the hiring enterprise affected interstate commerce. He said such an effect could be minimal. The government cited the out-of-state vendor the Probation Department utilized in its ankle bracelet monitoring program to monitor offenders. Hiring for the program, which was created under O’Brien’s watch, was part of the government case. The government also has to show, Young said, that those charged engaged in a “pattern of racketeering activity.” For O’Brien, he said, that must include at least two acts within 10 years of each other, and at least one must be more recent than March 2007, the outer bound of the five-year statute of limitation leading up to the date of the indictment in March of 2013.

Tavares is also charged with “aiding and abetting,” a charge that Young said does not require proof of her central involvement in the scheme, but only that she understood that a fraudulent scheme was in operation and acted in some way to further its operation. That involvement, he said, could be as limited as pushing hiring files through the system.

O’Brien is also facing bribery charges in connection with the government’s allegation that, together with House Speaker Robert DeLeo and DeLeo aide Leonard Mirasolo, he essentially gave lawmakers jobs to hand out at the state’s new electronic monitoring center in Clinton in exchange for their support for DeLeo, then the House Ways and Means Committee chairman, in his effort to be elected House speaker.

Neither DeLeo nor Mirasolo are charged in the case, and DeLeo has lashed out at the US attorney’s office for what he says are entirely unsubstantiated allegations that he denies.

If they deem the bribery charges not proven, Young told the jurors they must consider as a “fallback” a lesser charge of providing an “illegal gratuity.”

The government also alleges that O’Brien provided an illegal gratuity to state Rep. Thomas Petrolati by hiring his wife to direct the Probation Department’s electronic monitoring office in Springfield.

Young spoke to the jury on Tuesday before turning the proceedings over to prosecutors and defense lawyers for their closing arguments. The jury will begin deliberating on Wednesday.

Young, a former state superior court judge who was appointed to the federal bench in 1985 by President Reagan, seemed to enjoy his moment at center stage. Before delving into the specific charges, he had the jurors all stand and face him and consider the weighty responsibility they carry. He quoted an admired fellow federal jurist, Richard Arnold, who died in 2004, on the sanctity of court proceedings as the place where justice is delivered. “There has to be a safe place, and we have to be it,” Young quoted him as saying.

He also explained the various standards the jury must use to weigh testimony and other evidence. He offered an analogy to explain the concept of drawing reasonable inferences that involved barley fields, which, Young noted approvingly, play a vital role in the making of a particularly agreeable form of whiskey.