Question: Who unanimously ruled that the president had to hand over the tapes?
About the article "Watergate scandal", section "Abstract".

Candidate passages:
The issue of access to the tapes went to the Supreme Court.
On July 24, 1974, in "United States v. Nixon", the Court, which did not include the recused Justice William Rehnquist (who had recently been appointed by Nixon and had served as Assistant Attorney General of the Office of Legal Counsel in the Nixon Justice Department), ruled unanimously that claims of executive privilege over the tapes were void.
They ordered the president to release them to the special prosecutor.
On July 30, 1974, President Nixon complied with the order and released the subpoenaed tapes for the public. 
The Watergate scandal was a major political scandal that occurred in the United States in the 1970s as a result of the June 17, 1972 break-in at the Democratic National Committee headquarters at the Watergate office complex in Washington, D.C., and the Nixon administration's attempted cover-up of its involvement.
The term "Watergate" has come to encompass an array of clandestine and often illegal activities undertaken by members of the Nixon administration.
Those activities included "dirty tricks" such as bugging the offices of political opponents and people of whom Nixon or his officials were suspicious.
Nixon and his close aides ordered harassment of activist groups and political figures, using the FBI, CIA, and the Internal Revenue Service.
The scandal led to the discovery of multiple abuses of power by the Nixon administration, articles of impeachment, and the resignation of Republican Richard Nixon, the President of the United States, on August 9, 1974—the only resignation of a U.S. president to date.
The scandal also resulted in the indictment, trial, conviction, and incarceration of 43 people, dozens of whom were Nixon's top administration officials.
The affair began with the arrest of five men for breaking and entering into the Democratic National Committee (DNC) headquarters at the Watergate complex on June 17, 1972.
The Federal Bureau of Investigation (FBI) connected cash found on the burglars to a slush fund used by the Committee for the Re-Election of the President, the official organization of Nixon's campaign.
In July 1973, as evidence mounted against the president's staff, including testimony provided by former staff members in an investigation conducted by the Senate Watergate Committee, it was revealed that President Nixon had a tape-recording system in his offices and he had recorded many conversations.
After a protracted series of bitter court battles, the U.S. Supreme Court unanimously ruled that the president had to hand over the tapes to government investigators; he ultimately complied.
Recordings from these tapes implicated the president, revealing he had attempted to cover up the questionable goings-on that had taken place after the break-in.
Facing near-certain impeachment in the House of Representatives and equally certain conviction by the Senate, Nixon resigned the presidency on August 9, 1974.
His successor, Gerald Ford, then issued a pardon to him on September 8, 1974.
The name "Watergate" and the suffix "-gate" have since become synonymous with political scandals in the United States and in other English- and non-English-speaking nations as well.
The Brethren is a 1979 book by Bob Woodward and Scott Armstrong.
It gives a "behind-the-scenes" account of the United States Supreme Court during Warren Burger's early years as Chief Justice of the United States.
Using Woodward's trademark writing technique involving "off-the-record" sources, the book provides an account of the deliberations leading to some of the more controversial Court decisions from the 1970s.
Among the cases with substantial treatment in the book was the decision in "United States v. Nixon" (1974), where the Supreme Court unanimously ruled that President Richard Nixon was legally obligated to turn over the Watergate tapes.
In 1985, upon the death of Associate Justice Potter Stewart, Woodward disclosed that Stewart had been the primary source for "The Brethren."
The court unanimously ruled that the plaintiff's civil rights had been violated. 
The European Court of Human Rights unanimously ruled that no violation of Article 8 occurred because the amount of physical or psychological harm that the law allows between any two people, even consenting adults, is to be determined by the State the individuals live in, as it is the State's responsibility to balance the concerns of public health and well-being with the amount of control a State should be allowed to exercise over its citizens.
More specifically, the Court ruled that the reasons that the police gave for confiscating the tapes were valid, and that the action was justified granted the number of charges that were brought against the applicants.
The ruling also questioned whether or not the tapes could be considered part of the applicants' private lives, because so many people were involved in the footage, as well as because the applicants made and distributed the recordings in the first place.
The Court stressed that the ruling in "Laskey, Jaggard and Brown v United Kingdom" should be seen as distinct from that in "Dudgeon v. United Kingdom", an earlier, similar case relating to sexual behavior between consenting adults.