The federal judge in the corruption trial of former Probation commissioner John O’Brien recused himself Thursday but not before excoriating defense attorneys for bringing the motion as retaliation for ruling against them in a number of prior motions.

US District Court Judge F. Dennis Saylor IV says he based his decision on the fact that the defense may call as a witness his colleague and friend US District Court Judge Timothy Hillman. In his order, Saylor wrote, “the test is that of a reasonable and objective observer who is fully informed of all the relevant facts,” who must decide if his friendship with Hillman could cloud his ability to be impartial.

But Saylor, noting defense attorneys knew at least 15 months before their claim that Hillman was a potential witness, made clear his anger over the timing of the motion for recusal and what he sees as the motive behind it. Saylor included in his ruling a description of what he calls repeated false assertions by defense attorneys in a meeting in his office that Hillman made a call on behalf of his own daughter to get a job with probation. Defense attorneys later formally withdrew that claim in writing.

Saylor said Hillman’s name was brought up as a witness only after he ruled against motions by the defense for a continuance and then denied a defense motion for recusal because Saylor was once a partner at the same firm as Paul Ware, the lawyer who authored the scathing independent report that led to O’Brien’s firing and subsequent indictment.

“Counsel acknowledge that they were well aware that Judge Hillman and I are colleagues on a relatively small court, and that we were the only two judges in Worcester (save the bankruptcy judge) for a period of more than six years,” Saylor wrote. “They contend, however, that they had no way of knowing that we had a friendly relationship until I specifically mentioned that fact during a hearing on January 24, 2014. That claim is scarcely credible. More to the point, it is objectively unreasonable.”

Saylor also granted a motion to delay the trial for one month, until April 28, while a new judge is seated and gets brought up to speed.

O’Brien and two top aides, Elizabeth Tavares and William Burke, are facing more than a dozen corruption charges stemming from a rigged hiring system at the Probation Department that favored candidates sponsored by elected and appointed officials. Prosecutors claim it was a fraudulent system designed to pump up the Probation budget and O’Brien’s autonomy in exchange for patronage hirings. Defense attorneys say they plan to call scores of witnesses, including Hillman, who referred or wrote recommendations for 22 people, to show it is the way things are done on Beacon Hill and in government in general.

In concluding that recusal was the right course, Saylor did little to hide his contempt for the defense team’s tactics that led him to that decision.

“Defendants’ recusal motions could hardly have been more ill-timed; the case was indicted nearly two years ago, and is now less than three weeks away from the start of trial,” Saylor wrote. “The government, not just the defendants, has an interest in a speedy trial, and for that matter so does the public. No matter where this case is reassigned, delays — possibly significant ones — are likely to follow. Another cost is that defendants will inevitably reap the full reward of an untimely tactical maneuver. Whether they deliberately waited to raise the issue, or held back out of inattention or negligence, is unimportant; the result will be the same.

“The resulting and inevitable delay in the trial of this matter is unfortunate. But the trial will begin at some point; that day will not be postponed forever.”