I would reverse the conviction appealed from and order a new trial because of the admission of the “expert” testimony of Detective Mauriello that in his opinion the defendant was a member of the “Ghost Shadows” gang. I do not believe such testimony as to a significant concrete fact, not within the personal knowledge of the witness, is a proper subject for opinion *355testimony by an expert witness. This is not testimony merely as to general conditions, the existence of gangs, the way they operate, division of territories, etc. This is fact testimony in the guise of opinion as to a particular defendant’s membership in a particular criminal organization.
Nor am I able to say that this was harmless error. It is true that the People’s chief witness Mok testified to all these facts. But he had himself been a member of a rival gang and had engaged in many criminal activities. It is also true that the detective gave the basis of his opinion, i.e., his observations of the defendant with known members of the Ghost Shadows.
The evidence as to defendant’s membership in the Ghost Shadows was significant in the case to show that he shared the criminal intent of the persons with whom he was alleged to be in company, and who did the actual shooting. The jury might well have drawn that inference of shared intent from the other evidence in the case without Detective Mauriello’s expert opinion. But I cannot say this expert opinion made no difference.
As I have said, Mok himself had a history of disreputable and criminal activities. The jury might have disbelieved him. Thus the expert testimony of the police officer probably strengthened the acceptability of Mok’s testimony and for all we know may have been decisive.
In his summation, the District Attorney said: “Again, you need not rely on the testimony of Mr. Mok alone as to the defendant’s membership in the Ghost Shadows, Detective Mauriello again testified on the basis of his experience, the defendant Tse, the defendant Ying and Mooi were all active members of the Ghost Shadows, acting in concert. The [sic; In?] methodical and orchestrated fashion, Tse, Ying and Mooi had now stalked their predator.”
Murphy, P. J., Bloom and Kassal, JJ., concur with Ross, J.; Silverman, J., dissents in an opinion.
Judgment, Supreme Court, New York County, rendered on April 14, 1981, affirmed.