At а jury trial held subject to the provisions of G. L. c. 278, §§ 33A-33G, on indictments charging arson and murder (in the second degree), the defendant was convicted of arson and manslaughter, and sentenced. He has briefed and argued several assignments of error concerning: (1) the partial denial of his pre-trial motion to suppress certain statements made by him after his arrest; (2) the exclusion of certain testimony offered by him at the hearing on the pre-trial motion and at trial; (3) the ruling by the judge at the pre-trial hearing that a Commonwealth witness was properly qualified to testify as an expert witness.
We summarize the pertinent evidence еlicited at both the pre-trial hearing and at trial. On the evening of January 8, 1972, members of the Boston fire department responded to a fire in a basement apartment at 28 Isabella *16 Street. A police officer who arrived at the scene was directed by one of the firemen to speak with the defеndant, who was standing alone on a traffic island located nearby. The officer approached the defendant and “asked him if he lived down there.” The defendant answered, “Yes.” The officer then asked what had happened, and the defendant responded, “We were fighting and throwing things around, so I set the сurtains on fire.” The officer immediately informed the defendant that he was under arrest for arson and, accompanied by another officer, proceeded to transport the defendant to a police station. The body of the deceased, who was the defendant’s roommate, was discоvered inside the apartment by the firemen. That fact was apparently communicated to the arresting officer during the ride to the station, but the officer did not so inform the defendant. During that ride the defendant repeatedly asked about his “friend.” The officers responded equivocally. The arresting officer testified at the pre-trial hearing that the defendant appeared to have been drinking but that his speech was coherent.
Upon arrival at the police station the defendant was taken to the “booking desk.” There he was first informed of his
Miranda
rights
(Miranda
v.
Arizona,
*17 When Officer Langill finished questioning the defendant, Sergeant Detective Whalen of the Boston police department homicide unit again informed the defendant of his Miranda rights, one by one, reading them to him from a printed card. He asked the defendant after each right was read, “Do you understand that?” Each time the defendant answered, “Yes.” He also informed the defendant that he was being charged with murder and arson. Hе thereupon proceeded to tape record the interview with the defendant. At one point during the interview, after having admitted starting the fire, the defendant indicated that he did not wish to be questioned further.
At the pre-trial hearing and at trial, the defendant offered the testimony of two physicians and a social worker to the effect that during late 1971 the defendant had undergone treatment for problems related to alcoholism and that Thorazine, a major tranquilizing drug, had been prescribed. The defendant testified only at trial.
1. The judge filed findings and rulings on the defendant’s motion to suppress. He denied the motion as to thе statements made to the arresting officer and to Officer Langill. As to the statements made to Sergeant Whalen, he ruled that “when the defendant stated that he did not want to talk any more, he was exercising a constitutional right he had under the Miranda case, and nothing he said after that at the interrogation is admissible in evidеnce. What he said prior to his statement that he did not want to talk any more is admissible.”
The defendant argues that his motion to suppress should have been granted as to statements made to Officer Langill and Sergeant Whalen because (1) there was no evidence on the record of an affirmative waiver of Miranda rights; (2) there was no evidence of a knowing and intelligent waiver; and (3) the Commonwealth failed to meet its burden of proving the validity of the alleged waiver.
*18
We note at the, outset that the defendant does not maintain that his statement to the arresting officer at the scene of the fire (“We were fighting and throwing things around, so I set the curtains on fire”) is inadmissible. In-culpatory statements such as these, voluntarily made long before the onset of “custodial interrogation,” are clearly admissible.
Miranda
v.
Arizona,
With respect to the statements made to Officer Langill of the arson squad, however, we must agree with the defendant. The judge’s finding that “the dеfendant was completely advised of his rights under the
Miranda
case and understood those rights” lacks support in the record before us.
1
As the
Miranda
case makes clear, a valid waiver cannot be presumed from a silent record.
Miranda
v.
Arizona,
With respect to the statements made to Sergeant Whalen of the homicide unit, our opinion is that the Commonwealth has clearly demonstrated a constitutionally permissible waiver. The criterion which the prosecution must meet in such situations is that of a preponderance of the evidence. Leg
o
v.
Twomey,
The trial judge had before him at the pre-trial hearing the uncontradicted testimony of Sergeant Whalen that the
Miranda
warnings were fully given, that the defendant stated that he understood them, that the defendant was informed of the charges against him, and that the defendant was willing to make a statement. Other testimony established that the defendant, who was talkative from the outset, was not misled or coerced by the interrogating officers, was not subjected to lengthy or brutal interrogation, was not incoherent, and was of sufficient maturity and intelligence to understand his position.
2
The trial judge is in a far better position to determine the existence of a knowing, intelligent and voluntary waiver than is an appellate court; his findings are entitled to “substantial deference.”
United States
v.
Springer,
The absence of a written waiver is not crucial if, as here, it can be found that in the circumstances a knowing and intelligent waiver took place.
United States
v.
Stuckey,
The defendant suggests that he may have been incaрable of making a knowing and intelligent waiver as there was evidence that he had been drinking during the day of the fire. Much of the evidence on that point, however, was introduced at trial and not at the pre-trial hearing on the motion to suppress. Compare
Eisen
v.
Picard,
We conclude that the trial judge’s rulings on the admissibility of the defendant’s statements to the arresting officer and to Sergeant Whalen were correct. His ruling on the admissibility of the statements to Officer Langill, although in our view incorrect, does not require reversal. In view of the evidence that the interrogations were brief and neither physically nor psychologically coercive, and thаt the defendant provided no significant details in his statement to Officer Langill that were not related in the other two statements, we think this case is a proper one for the application of the harmless constitutional error standard enunciated by the United States Supreme Court in
Chapman
v.
California,
2. The defendant assigns as error the exclusion of testimony at the pre-trial hearing and at trial of two witnesses, a physician and a social worker.
a. Testimony of the Physician.
A physician, called as a witnеss by counsel for the defendant, testified at the pre-trial hearing that he was in his third year of resident training in psychiatry at the Boston University Medical Center; he described his qualifications in detail. He testified that he had seen the *22 defendant once, on the evening of December 31, 1971, when the defendant had been brought tо the hospital by a clergyman. The witness was unable to conclude that the defendant had been drinking, but he did make a psychiatric diagnosis of the defendant. His testimony as to his diagnosis was excluded at the pre-trial hearing as well as at trial. In each instance the defendant saved an exception. The defendant made an offer of proof that the doctor would have testified that the diagnosis was one “of acute borderline psychotic episode in the [morning], and chronic mixed characterological pathology.” The judge stated at the hearing that he did not find the witness qualified. The witness was pеrmitted to testify that he had recommended that the defendant be committed to Boston State Hospital.
It is well settled that it is the duty of the trial judge to determine whether an expert witness is properly qualified.
Commonwealth
v.
Spencer,
b. Testimony of the Social Worker.
A social worker at the South End Medical Center for Alcoholics was also called as a witness for the defense. She testified that she had first seen the defendant threе years earlier, when he had been referred to the Center. She testified that the defendant was an alcoholic when he *23 came to the Center and that she counseled him “as an alcoholic” during the year 1971. She also testified as to the defendant’s behavior and emotional state when he aрpeared to be under the influence of alcohol. She stated that she last saw the defendant on January 3, 1972, five days before the fire, and that at that time he was under the influence of alcohol and drugs. She was not permitted to testify whether, in the course of counseling the defendant, she had formed an оpinion that he was an alcoholic. The defendant’s exception was saved. The witness had already testified, without objection, that the defendant was an alcoholic, and that she had counseled him as an alcoholic. Thus, the substance of the proffered testimony had already been conveyed to the jury. Our opinion is that the question was properly excluded.
At the pre-trial hearing this witness was not permitted to answer a question calling for her opinion of the defendant’s “mental status” at a time shortly before the fire. That vague question called upon the witness to give an expert’s opinion аnd, for the reasons stated above concerning the physician’s testimony, was properly excluded.
3. The defendant assigns as error the determination by the trial judge at the pre-trial hearing that Officer Langill of the arson squad “was qualified as an expert to give an opinion concerning the origin of the firе.” We reiterate that the determination of whether an expert is properly qualified is for the trial judge to make and that his decision is ordinarily conclusive unless erroneous in law.
Commonwealth
v.
Spencer, supra.
“The conclusion of the trial judge that a witness is competent to express an opinion upon a particular matter сan be disturbed only where there is no evidence to warrant that conclusion.”
Commonwealth
v.
Bellino,
Commonwealth
v.
Rucker,
Judgments affirmed.
Notes
It would appear from Officer Langill’s testimony at the pre-trial hearing that the Miranda warning was not fully administered in that the warning as to the right to have counsel appointed was omitted. Officer Langill testified at trial that he advised the defendant of all the Miranda rights, including the right to have counsel appointed. Our consideration of the adequacy of the warnings must be limited to the evidence adduced at the pre-trial hearing.
Contrast such cases as the following in which no valid waiver was found:
Eisen
v.
Picard,
Officer Langill and Sergeant Whalen both testified that they were unable to form an opinion as to whether the defendant had been drinking.
