ST. LOUIS -- A Missouri death row inmate testified Wednesday that he was beaten so badly during an interrogation by detectives that he admitted to a role in a horrific crime.

But when an assistant attorney general repeatedly asked Reginald Clemons about details of the 1991 rape and murder of two sisters, Clemons time and again declined to answer, citing his constitutional right against self-incrimination.

A specially-appointed judge is hearing the case in St. Louis, then will issue a report to the Missouri Supreme Court. Clemons' attorneys are seeking to get his death sentence commuted and also asking for a new trial. The civil hearing is expected to wrap up this week, but the Supreme Court likely won't make a decision for several months. The case has drawn attention from death penalty opponents from around the world.

Clemons, now 41, was one of four men convicted in the killings of 20-year-old Julie Kerry and 19-year-old Robin Kerry. In April 1991, the sisters and their cousin, Thomas Cummins, were pushed off an abandoned bridge into the Mississippi River in St. Louis. Cummins survived.

Clemons testified for more than two and a half hours Wednesday, quietly recalling how he was home in his basement preparing to go to work to deliver pizzas when his mother called him upstairs. A police detective wanted to talk to him, but didn't say why as he drove him to the St. Louis police station.

"That was the last time I was home," Clemons said.

Clemons said once he learned of the seriousness of the allegations, he requested a lawyer, but was told he couldn't have one. So he stopped talking.

That's when the two detectives interrogating him became aggressive, Clemons said. He said he was repeatedly struck in the head, face, chest, side and stomach.

The body blows were especially frightening, Clemons said, because he suffered from asthma so bad he often required hospitalization.

"It reached a point where I couldn't take it anymore," Clemons said. "I could have taken the pain, but the thing that frightened me the most was if I started having an asthma attack, I could end up suffering and dying."

Confessing, he said, "was the only way I could think of to get them to stop beating me." He agreed to confess to rape, but not murder.

Assistant attorney general Sue Boresi played the audiotaped confession. On it, Clemons gave a detailed account of how he and three friends -- Marlin Gray, Antonio Richardson and Daniel Winfrey -- visited the closed Chain of Rocks Bridge. There, they encountered the Kerry sisters and Cummins. Gray suggested raping the girls, Clemons said in the confession.

Clemons described on the tape how Cummins was forced to the ground and he stood over him while Gray and Richardson raped the girls. When they were done, Clemons said, he raped Robin Kerry.

The men then decided to kill the trio and led them from the bridge deck through a manhole cover to a structure below the deck, Clemons said on the tape. He said Richardson pushed both girls into the river. Cummins jumped.

Julie Kerry's body was found three weeks later, 150 miles downriver. Robin Kerry's body was never recovered. Cummins was able to swim to shore.

After playing the tape, Boresi asked Clemons 32 questions about the events that occurred that night. For each question, he answered, "Under the advice of counsel I plead the Fifth."

Jackson County Circuit Judge Michael Manners reminded Clemons about the potential repercussions of invoking his right against self-incrimination in a civil proceeding.

"You understand that the inferences I will draw from your testimony will be unfavorable to you," he told Clemons and gave him the lunch break to reconsider.

Afterward, Clemons agreed to answer three questions, denying that he helped lead the victims to the bridge support, and twice denying that he blocked the manhole to prevent their escape.

In addition to the alleged coerced confession, Clemons attorney Josh Levine has expressed many other concerns, including the original prosecutor's failure to alert defense attorneys to a medical examiner's test that showed no evidence that Julie Kerry was raped. Boresi said the body had been in the river so long that determining rape was impossible.

Gray was executed in 2005. Richardson is serving life in prison after his death penalty was overturned because of a procedural error. Winfrey pleaded guilty to second-degree murder after agreeing to testify against the others. He was released on parole five years ago.