WASHINGTON Death penalty challenges from two Wichita brothers convicted of a notorious rape-and-murder spree seemed to sputter Wednesday before skeptical Supreme Court justices.

Even several liberal justices sounded doubtful about some arguments raised by attorneys for Reginald Carr Jr. and his younger brother Jonathan, while conservative justices all but announced their support for the Kansas prosecutors who secured death sentences for both Carrs.

Underscoring the court's apparent tilt, Justice Antonin Scalia took the unusual step of reading, at length, a detailed account of what the Carrs did in December 2000. Scalia pulled few punches in casting doubt on defense arguments.

"You truly think that this jury ... would not have imposed the death penalty?" Scalia asked a defense attorney, following the recitation of gruesome facts.

Attorney Frederick Liu countered that Scalia himself in an earlier decision noted "the egregiousness" of an offense is just one factor considered when sentences are set. The Kansas cases argued Wednesday focused on two distinct procedural issues that affect sentencing.

"The crimes in this case were horrific," Liu said, "but that is just one side of the scale."

One issue weighed over the course of two hours was whether the trial judge left jurors confused about what standard of proof applied to the mitigation evidence presented during sentencing by the Carrs' defense attorneys. The other issue was whether the judge erred in refusing to sever the sentencing proceedings, so that each brother would receive his own hearing.

Both issues touch on the Eighth Amendment's prohibition on cruel and unusual punishment.

In a tag-team performance, Kansas Attorney General Derek L. Schmidt argued the trial judge's mitigation instructions were sufficiently clear, while Kansas Solicitor General Stephen R. McAllister defended the use of a single sentencing hearing.

"These sentences do not offend the Eighth Amendment," Schmidt told the justices. "The verdicts reflect the reasoned moral response of these jurors to the aggravated brutality of these crimes, the weak claims for mitigation and the individual assessment of each (man's) moral culpability."

The Carr brothers were convicted and sentenced to death for a string of crimes in December 2000. Most infamously, in what became known as the "Wichita Massacre," the two men invaded a home in the city's Birchwood neighborhood.

There, over the course of about three hours, they forced three male residents to have sex with two women who were visiting. They compelled the two women to have sex with each other. Jonathan raped one woman and attempted to rape the other. Reginald raped one of the women.

The Carrs then drove the five victims to a soccer field, ordered them to kneel in the snow and one of the brothers shot each victim in the back of the head. One woman, named Holly, survived when the bullet apparently bounced off a plastic hair clip she was wearing.

"These cases involve some of the most horrendous murders that I have seen in my 10 years here," Justice Samuel Alito Jr. said, "and we see practically every death penalty case that comes up anywhere in the country. These have to rank as among the worst."

Reginald, sometimes known as "Big Smoke," was 23 at the time. Jonathan was 20.

"The state never established the identity of the shooter," defense attorney Jeffrey T. Green noted Wednesday.

The two brothers were tried jointly. Once convicted, they also faced a joint sentencing phase even though they asked the judge to sever the proceedings. The Obama administration, supporting Kansas on this issue, urged the court to accept as reasonable the trial judge's decision.

"Joint proceedings can enhance fairness and accuracy," argued Rachel P. Kovner, assistant to the U.S. solicitor general, adding "they prevent arbitrary disparities that may arise when two juries reach inconsistent conclusions about the common facts of a single crime.

Tellingly, liberal Justice Stephen Breyer added "severance is very, very rare, and joint trials are common."

Both brothers presented mitigating evidence their terrifying childhood had been rife with physical, sexual and drug abuse, with Jonathan presenting additional evidence his older brother had been a corrupting influence.

The judge did not specifically inform jurors they did not have to hold the mitigating evidence to the same beyond-a-reasonable doubt standard required of the prosecution's evidence at trial. Defense attorneys say that raises the possibility jurors mistakenly applied a higher standard to the mitigating evidence and so potentially threw some out.

"A man is being put to death under jury instructions that are so confusing that there is a reasonable likelihood that some juries would interpret those instructions to bar consideration of the mitigating circumstances and others would not," defense attorney Neal K. Katyal said.

The same jury instruction issue also arose in a parallel Kansas death penalty case considered Wednesday, involving Sidney J. Gleason, convicted of murder in a February 2004 incident in Great Bend. The less sensational facts in Gleason's case did not get the same attention Wednesday.

Schmidt noted since the Carr brothers were tried, the state of Kansas has changed its procedures to require explicit jury instructions.

Sounding somewhat sympathetic to Schmidt's argument, liberal Justice Elena Kagan added that while some of the Carr jury instructions might have been "unfortunate," other instructions concerning issues like "mercy" suggested the possibility that "that no juror was likely to be confused."

Justice Clarence Thomas, as is his customary practice, was the only one of the nine justices not to speak or ask any questions during the two-hour argument. Thomas is a consistent death penalty supporter.

A court decision is expected before the current term ends June 30, although it could come much sooner than that.