In
Commonwealth
v.
Pisa,
*725
The homicide took place in 1969, and the defendant was convicted in 1970. One White was tried separately in 1971 for the same homicide, and his conviction of murder in the second degree was affirmed in
Commonwealth
v.
White,
We summarize the master’s findings. In 1973 the lawyer in question, then a law student, worked as a research assistant for the defendant’s counsel, preparing a memorandum of law in support of the defendant’s motion for a new trial. He had access to the defendant’s file and was present at discussions between the defendant and his counsel, but had no knowledge of the case that was not disclosed in the prоceedings on the motion. In the fall of 1974, after passing the bar examination, the lawyer joined the office of the district attorney in Middlesex County, and informed those in charge that he could not write briefs in certain cases, including the Pisa сase.
In May, 1976, an assistant district attorney was writing the Commonwealth’s brief in Pisa’s appeal to this court. 1 She asked the lawyer to proofread the typed manuscript for typographical and grammatical errors and to cheсk citations. He did so. He provided no confidential information, did no research, and made no changes. The typing was completed on Friday, June 4, 1976, the day the brief was to be filed, and it was checked and printed the same day. The following Monday the assistant district attorney and the lawyer learned for the first time, as a result of an inquiry from defendant’s counsel, that both their names had been printed on the brief. The assistant district attorney told defendant’s counsel that she, not the lawyer, had *726 written the brief, and the defendant’s counsel accepted her explanation without further inquiry. The special master concluded that what the lawyer did "was minor and inconsequential” and that "it, beyond any reasonable doubt, was a completely harmless mistake of judgment for him to proofread the brief.”
1.
The impropriety.
We state with emphasis that the situation disclosed by the present record should never have arisen. It is common ground that the lawyer in question, having participated in the preparation of the defendant’s case, could not properly participate in the prosecution of the defendant. The principle is clear that a lawyer who represents a client in litigаtion should not thereafter represent an adversary in the same case. That principle is in part, but only in part, "a strict prophylactic rule to prevent any possibility, however slight, that confidential information acquired from а client during a previous relationship may subsequently be used to the client’s disadvantage.”
Ernie Indus., Inc.
v.
Patentex, Inc.,
In the context of civil aсtions conducted by private law firms the principle is enforced with rigor. It has been applied to associate counsel and law clerks and perhaps to others who have access to confidential information,
*727
even though their work is nonlegal.
Consolidated Theatres, Inc.
v.
Warner Bros. Circuit Management,
The application of the principle
to
public officials is somewhat less rigorous. See
United States
v.
Standard Oil Co.,
2.
Prejudice.
The rules of disqualification we have outlined are primarily designed to avoid conflicts of interest before they arise. On a motion to disqualify a lawyer from participating in a proceeding there is no weighing of the probabilities that actual harm will result from his participation. The rules are applied not only to prevent prejudice to a рarty, but also to avoid even the appearance of impropriety.
Emle Indus., Inc.
v.
Patentex, Inc., 478
F.2d 562, 570-571 (2d Cir. 1973). A case stands in a different posture when there has been no disqualification
*729
and the rules are used to attack a criminal conviction. Cf. S.J.C. Rule 3:22A,
When the impropriety is a conflict of interest on the part of a defendant’s trial cоunsel, it may be impossible to identify from the record the resulting prejudice. The formation of the record itself might be affected by decisions influenced by the conflict. In such a case, inquiry by an appellate court into prejudicе would require "unguided speculation.”
Holloway
v.
Arkansas,
Prosecutоrial conflicts of interest are treated with similar strictness. No showing of prejudice is required when the prosecutor has a personal interest in the outcome of a criminal trial.
Commonwealth
v.
Tabor,
When a defendant’s lawyer switches sides, the principal danger is that informаtion supplied in confidence will be used to the defendant’s disadvantage. That danger is greatest when the lawyer switches sides prior to trial, and is in a position to use confidential information in his formulation of strategy and developmеnt of the facts. Resulting prejudice could be impossible to assess. But see
Manuel
v.
Salisbury,
In the presеnt case, there is no contention that a conflict of interest affected the trial in any way. Nor does the defendant contend that the lawyer was an agent for the prosecution who sabotaged the motion for a new trial. Cf.
Commonwealth
v.
Manning,
Notwithstanding the impropriety, the appeal resulted in a reduction of the defendant’s conviction. It is conceivable that in some cаses confidential information might be useful even on appeal. But in this case, we cannot see how information not in the record could have helped the prosecution. The special master’s careful findings on the extеnt of the lawyer’s participation in the case foreclose any possibility that the impropriety was prejudicial.
We in no way condone the conduct of the prosecution in the present case. The assistant district attorney should not have asked the lawyer to perform any tasks in connection with the brief. The lawyer should have refrained from any participation in the appeal. But his participa
*731
tion was minimal and resulted in no harm to the defendant. Not every violation by a prosecutor of rules of professional conduct requires reversal of a conviction.
People
v.
Green,
3. Other issues. Other allegations of impropriety made in the defendant’s brief relate to the conduct of the master and the single justice who confirmеd the master’s report. The Commonwealth moved to strike these portions of the brief. We deny that motion, and allow the defendant’s motion to expand the record to include an affidavit of his former counsel. We have given the defendant’s arguments full consideration, and find them to be without merit.
Judgment affirmed.
Notes
A different assistant district attorney appeared for the Commonwealth in the present appeal.
