opinion: Mr. Chief Justice Burger
  delivered the opinion of the Court.
  We granted the writ of certiorari on claims under the Fifth and Sixth Amendments arising out of the use of one of a number of confessions, all of which were received in evidence over objection. The confession challenged here was obtained by a police officer posing as an accused .person confined in the cell with petitioner.
  Petitioner Milton is presently serving a life sentence imposed in 1958 upon his conviction of first-degree murder following a jury trial in Dade County, Florida. During that trial, the State called as a witness a police officer who, at a. time when petitioner had already been indicted and was represented by counsel, posed as a fellow prisoner and spent almost two full days sharing a cell with petitioner. The officer testified to incriminating statements made to him by petitioner during, this period. Contending that the statements he made to the officer were involuntary under Fifth Amendment standards and were obtained in violation of his' Sixth Amendment rights as subsequently interpreted in Massiah v. United States, 377 U. S. 201 (1964), petitioner initiated the present habeas corpus proceeding in the United States District. Court for the Southern District of Florida. The District Court, finding that petitioner had exhausted his state remedies in the course of several post-conviction proceedings in the Florida courts, ruled against petitioner on the merits of his claim, holding that his statements to the police ■officer were not inadmissible on Fifth Amendment grounds and that his Sixth Amendment claim could not prevail since “[n]o Court has declared Massiah retroactive, and .this Court will not be the first to do so.” 306 F. Supp. 929, 933. The Court of Appeals affirmed the denial of relief to petitioner, 428 F. 2d 463.
  On the basis of the argument in the case and our examination of the extensive record of petitioner’s 1958 trial, we have concluded that the'judgment under review must be affirmed without reaching the merits of petitioner’s present claim. Assuming, arguendo, that the challenged' testimony should have been excluded, the record clearly reveals'that any error in its admission was harmless beyond a reasonable doubt. Harrington v. California, 395 U. S. 250 (1969); Chapman v. California, 386 U. S. 18 (1967). The jury, in addition to hearing the challenged testimony, was presented with overwhelming evidence of petitioner’s guilt, including no less than three full confessions that were made by petitioner prior to his indictment. Those confessions have been found admissible in the course of previous post-conviction proceedings brought by petitioner in his attempts to have this conviction set aside, and they are not challenged here.
  The crime for which petitioner was convicted occurred in the early morning hours of June 1, 1958. The woman with whom petitioner had been living was asleep while riding as a passenger in the rear seat of an automobile driven by petitioner; she died by drowning when the car ran into the Miami River with its rear windows closed and its rear doors securely locked from the outside with safety devices designed to ensure against accidental'opening of the doors. Petitioner, who jumped from the-car shortly before it reached the water, was nevertheless propelled into the river by the car’s momentum; he was recovered from the water when a seaman nearby heard his cries for help and found him clinging to a boat moored in the river near the point of the automobile’s entry. A few hours later the car, with the victim’s'body still inside, was retrieved from the bottom of the river a short distance downstream from its point of entry.
  The following day the Miami police arrested petitioner on manslaughter charges and placed him in the city jail. Ten days after the woman’s death; petitioner, having been. advised of his right to remain silent, confessed that he had deliberately killed the woman and. that the accident was simulated.' He first made an oral confession to a police officer during- a question-and-answer exchange that was preserved on a wire-recording device. He then repeated his confession during another exchange and these statements were taken down by a stenographer; after this stenographic recording was converted to a transcript, petitioner read it over in full and signed it at 11 p. m. on June ll.
  The following day, petitioner told a police officer that he would like to make some clarifying additions to the statements in the writing he had signed the previous night. The officer suggested that they first go with a photographer to the scene of the incident “and reconstruct how this thing . . . occurred.” Petitioner agreed. Hé, the police officer, and a photographer then went to the scene of the crime where petitioner pointed out the route he had taken in driving the car to the river, the.approximate point at which he had jumped out of the car, and the point of the car’s entry into the river. Petitioner was then taken back to the police station where he went over his statement of the night before and indicated to the officer the' parts of that statement he wanted to clarify. Once again, a stenographer was summoned and a question-and-answer exchange was taken down and transcribed to-a writing that petitioner read over and signed. Approximately one week after he had made these confessions, petitioner secured the services of an attorney who advised him not to engage in any further discussions of his case with anyone else.
  Following this, and while petitioner was under indictment and confined in the Dade County jail awaiting trial, the State, for reasons that are not altogether clear, assigned a police officer named Langford the special detail of posing as a prisoner and sharing petitioner’s cell in order, to “seek information” from him.
  ■ Langford entered the cell with petitioner late one Friday afternoon and presented himself as a fellow prisoner under investigation for murder; he assumed a friendly pose toward his cellmate, offering petitioner some of his prison food at their first breakfast together the next morning and telling petitioner something of his own fictitious “crime,” which he described as a robbery committed with an accomplice who had used Langford’s gun to kill the robbery victim. Finally, petitioner began to boast that he had not made Langford’s mistake of having an accomplice who might later serve as a witness; instead, he said, he had committed the “perfect” crime with no surviving witnesses. By the time Langford left, the cell on Sunday afternoon, petitioner had described his own crime in some detail and had predicted with much assurance that he would soon be released, that he would collect a lot of insurance money, and that he would then flee the State with the insurance money without ever being brought to trial for his “perfect” crime. The incriminating statements made to Langford were essentially the same as those given in the prior confessions not challenged here.
  At petitioner’s trial-in state court, the wire recording of his first, confession was played back, first to-the judge for a ruling on its admissibility,, and then to the jury. Petitioner’s two written confessions were also- received in evidence, as were the photographs that were taken and the statements that, were made by petitioner when he reconstructed the crime at the scene of its occurrence. In addition, Langford was permitted to testify to the statements made to him by petitioner while the two men were sharing the cell in the county jail. Other evidence, highly damaging to petitioner in its totality, was also presented to the jury. For example, there was testimony that petitioner had told an acquaintance a few months before the murder that he disliked Minnie Claybon (the murder victim) and was interested only , in getting some money out of her. The terms of certain insurance policies- purchased by petitioner about two months before the crime were described in testimony given by the selling insur-aneé agents; the policies provided for the payment of $8,500 to -petitioner upon the accidental death of Miss Claybon, • and the agents testified that petitioner had faithfully maintained his weekly premium payments on the policies. Other testimony, however, indicated that petitioner was hard pressed for money shortly before'the murder, having fallen behind in his rent payments and having sold some of his personal clothing to raise small sums. There was testimony that petitioner had purchased the car in which Miss Claybon drowned on the very afternoon before the crime, making a cash down payment of $8; that the safety devices on the rear doors» of the car had been left in the unlocked position by the car’s former owner; that these devices could be put in the locked position only by loosening'a screw, _ sliding the locking device into position, and then retightening the screw; and that these devices were found securely screwed in the locked position when the car, with the victim’s' body still inside, was recovered from the river. After hearing all the evidence, the jury found petitioner guilty of murder in the first degree, but recommended mercy; on that recommendation, the trial judge imposed the sentence of life imprisonment.
  The petitioned has made a number of collateral attacks on his conviction, primarily in the courts of Florida. In response to one of his applications for post-conviction relief, the Florida Supreme Court issued a writ of habeas corpus, heard oral argument on the voluntariness of petitioner’s wire-recorded and written confessions, but thereafter. discharged the writ in a reported decision upholding the voluntariness of those confessions and their admissibility at trial. Milton v. Cochran, 147 So. 2d 137 (1962), cert. denied, 375 U. S. 869 (1963). The issues raised in that proceeding are not now before us and must, for the purposes of the instant case, be treated as having been properly resolved by the Florida Supreme Court. Cf. Sup. Ct. Rule 23 (1)(c).
  In initiating the present habeas corpus proceeding in the District Court, petitioner sought to have his conviction set aside on the ground that the statements he made to police officer Langford should not have been admitted against him. Our reviéw of the record, however, leaves us with no reasonable doubt that the jury at petitioner’s ■ 1958 trial would have reached the same verdict without hearing Langford’s testimony. The writ of habeas corpus has limited scope; the federal courts do not sit to re-try state cases de novo but, rather, to review for violation of federal constitutional standards. In that process we do not close our eyes to the reality of overwhelming evidence of guilt fairly established in the state court 14 years ago by use of evidence not challenged here; the use of the additional evidence challenged in this proceeding and arguably open to challenge was, beyond reasonable doubt, harmless.
  Affirmed.
  In this first written confession, petitioner made the following statements:
  “Minnie Lee Claybon [the murder victim] and myself had an insurance policy together. So I started thinking about the insurance and the money that I could get if something happened to her. I knew that I could use the money if something happened. So I decided to do something about it one way or the other, so one night we had been riding around in the car. So I decided to get the whole thing over with. So I drived the car into the river and she was killed. ■
  “. . . I drove the car straight toward the river, and just as I got almost to. the river, ... I jumped from the car and the car went on into< the river and I skidded and kept rolling over and over-until I was in the river also. I hurt my shoulder. I couldn’t move • that arm. It was hurting real bad.”
  In this second writing, petitioner confirmed in major part the statements he had made the night before, but said in addition that he had “decided to kill” the woman “about a month before this incident happened.” He further stated, however, that he was not thinking of the insurance money when he made that decision, but was thinking instead of the woman’s habits of associating with other men, drinking too much, and staying out late at night. He reaffirmed in express terms that he, had deliberately driven the car into the river with the intention of killing the woman.
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