Specifically, the Sixth Amendment gives the defendant the right "to be confronted with the witnesses against him" so a defense lawyer can cross examine those witnesses and juries can evaluate witness statements in deciding guilt or innocence.
Fairly or not, jurors in Peterson's trial said hearsay statements by his third and fourth wives -- one murdered and the other presumed dead -- weighed heavily in their guilty verdict.
The answer, of course, is that the protections of the confrontation clause aren't absolute.
State law and U.S. Supreme Court precedent allow for exceptions, and with Peterson defense lawyers vowing to appeal, the high court may be the ultimate arbiter of whether his conviction was constitutional and should be upheld.
As Peterson, 58, sat glaring from the defendant's chair, a state jury in Joliet Sept. 6 convicted the former suburban Chicago police sergeant of killing his third wife and staging her death to look like an accident. Peterson now faces a possible 60 years in prison when sentenced in late November.
The Will County jury of seven men and five women deliberated nearly 14 hours over two days following a monthlong trial before convicting Peterson of first-degree murder in the death Kathleen Savio, whose body was found in a dry bathtub in 2004.
Savio's death initially was ruled accidental. The case was reopened after the disappearance of Peterson's 23-year-old fourth wife, Stacy Peterson, and the 40-year-old Savio's body was exhumed for further examination.
Will County State's Attorney James Glasgow said autopsies during the re-examination of the death showed Savio "was violently drowned by another person and all the evidence points to this defendant. ... This defendant brutally killed Kathleen Savio."
However, besides the autopsies much of the case against Peterson depended on hearsay statements from Savio and Stacy Peterson that would have been prohibited from use as evidence in the past.
After Savio's death, while police were looking for Stacy Peterson, the Illinois Legislature in 2008 enacted a law, now popularly known as "Drew's Law," allowing jurors to consider hearsay statements from "unavailable witnesses" if those witnesses were killed to prevent their testimony and the hearsay statements were "reliable."
Jurors later told The Huffington Post they were troubled by the prosecution's reliance on hearsay but reports elsewhere last week indicated statements by a divorce attorney consulted by Stacy Peterson were instrumental in the conviction.
Attorney Harry Smith testified Stacy Peterson asked him if she could get more money in a divorce settlement if she threatened to tell police she knew how Peterson killed Savio.
The last holdout for a guilty verdict, juror Ron Supalo, who told The Huffington Post, "I needed time to think it through." The U.S. Postal Service letter carrier said he believed the state hearsay law might be unconstitutional, but his duty as a juror was just to assess the evidence.
"We [the jurors] weren't the U.S. Supreme Court," he told the website. "Right or wrong, this was the hearsay law, and we had to use it in this case." Prosecutors argued hearsay evidence would allow Savio and the missing Stacy Peterson "to speak from their graves."
Jury foreman Eduardo Saldana, 22, told the website the women's reported statements were "extremely critical" in deliberations and in his decision to convict Peterson.
During the trial, the Rev. Neil Schori testified Stacy Peterson told him weeks before she disappeared in 2007 her husband left their house about the time of Savio's death, then came back and stuffed women's clothing in their washing machine. Schori also testified Stacy Peterson said her husband coached her for hours on how to lie to police.
"I'm uncomfortable with the Illinois law that allowed hearsay," Supalo told The Huffington Post. "They made the law just for Drew Peterson, applied it to him retroactively. If there was no hearsay in his case -- Drew Peterson goes free."
"When Stacy couldn't find him, and he showed up by the washing machine with women's clothing and told her she was going to be interviewed by police, that was kind of key evidence," ABC news quoted juror Theresa Mathews as saying.
Also, "one thing Drew said when he was going up the stairs [that night] was, 'They're going to think I did it.' That kind of confirmed it for us," Saldana said.
The U.S. Supreme Court constructed a principle for the admission of hearsay evidence in 1980s Ohio vs. Roberts.
In that case, an Ohio man was accused of check fraud and possession of someone else's credit cards. During a preliminary hearing, the victim's adult daughter testified she had allowed the defendant to use her apartment, but denied she gave him the credit cards and checks and denied she gave him permission to use them. She wasn't cross-examined.
At trial, the defendant said the daughter had given him the checks and cards and permission to use them. Though prosecutors issued five subpoenas, the daughter disappeared and didn't testify. But relying on an Ohio statute that permits the use of such testimony when the witness "cannot for any reason be produced at the trial" -- the only indication of her whereabouts was word from a San Francisco social worker that she had applied for welfare -- prosecutors used a transcript of her earlier statements at trial.
A state judge admitted the transcript into evidence, but the Ohio Supreme Court eventually ruled the transcript was inadmissible because the daughter had not been actually cross-examined at the preliminary hearing, and was absent at trial. Therefore, the admission of the transcript violated the defendant's confrontation right.
The U.S. Supreme Court reversed.
The justices ruled 6-3 that when a hearsay witness is not present for cross-examination at trial, the hearsay statement is still admissible when there is a "showing" the witness is unavailable and if the statement has an "indicia of reliability."
The daughter's statement showed that "indicia of reliability," the majority opinion written by Justice Harry Blackmun said, and was therefore constitutional.
Twenty-four years after Ohio vs. Roberts, the U.S. Supreme Court fine tuned that principle. The justices unanimously ruled in Crawford vs. Washington "the only indicium of reliability sufficient to satisfy constitutional demands is confrontation" -- in other words, there had to be some cross-examination of the original statement in order for it to be used later, something obviously not present in the hearsay statements used in the Peterson trial.
In that 2004 Washington state case, a man accused another man of attempting to rape his wife, then got into an argument with the victim and stabbed him. The suspect told police he thought the victim had a weapon at the time of the argument, but couldn't be sure later. The suspect's wife told police, after first denying she had seen the fight, that she had indeed seen the fight and the victim did not have a weapon.
The wife did not have to testify against her husband at trial because of the "spousal exemption," but her statement to police was introduced.
State courts upheld the conviction, relying on Ohio vs. Roberts to weigh hearsay evidence.
The U.S. Supreme Court reversed, saying the use of the wife's statement "violated the confrontation clause because, where testimonial statements are at issue, the only indicium of reliability sufficient to satisfy constitutional demands is confrontation."
After discussing the history and meaning of the confrontation clause, the opinion by Justice Antonin Scalia said: "The [Ohio vs.] Roberts test departs from historical principles because it admits statements consisting of ex parte [outside the court] testimony upon a mere reliability finding. ... The unpardonable vice of the Roberts test is its demonstrated capacity to admit core testimonial statements that the confrontation clause plainly meant to exclude."
Hearsay was also touched upon when in 2006 the high court struck down the Guantanamo military commission trials established by presidential order -- as opposed to commissions later set up by Congress in a law.
In Hamdan vs. Rumsfeld, the majority 5-3 opinion written by Justice John Paul Stevens (Chief Justice John Roberts withdrew from the case) said the problem with the process ordered by the president was that the "commission's procedures ... provide, among other things, that an accused and his civilian counsel may be excluded from, and precluded from ever learning what evidence was presented during any part of the proceeding [depending on whether] the official who appointed the commission or the presiding officer decides to 'close' [the proceedings]."
In other words, the commission detainees not only had no right to confront their accusers, they may not even know who was doing the accusing or what was being alleged.
None of the three cases -- Ohio vs. Roberts, Crawford vs. Washington or Hamdan vs. Rumsfeld -- is strictly analogous to the Peterson case, which deals with hearsay "voices from the grave." But together they give an idea of Supreme Court thinking should the Peterson case and an Ohio law similar to "Drew's Law" come before the justices for review.
2014: The Year in Music [PHOTOS]