Who is responsible for the life of a child? Her parents or her school or her church? Some would suggest that each of us, even strangers, is responsible for what we see with our eyes and know in our hearts, that human decency would compel us to protect a child in mortal danger.

Let us go now to the Primadonna Resort and Casino in Primm, Nevada, a dusty place near the California border, about 40 miles from the glamour of Las Vegas. Still, they make an effort. Here they feature Rebecca's Oyster Bar, and the shows are pretty upscale (soul singer James Brown is playing next week).

But it is the casino that draws Californians to gamble away a pay cheque - or strike it rich.

On May 25th last year, a bank holiday weekend, Leroy Iverson took his seven-year-old daughter, Sherrice, and her 14-year-old half brother to Nevada. Sherrice's mother, Yolanda Manuel, a 28-year-old cafeteria worker, was back home in Los Angeles.

Mr Iverson spent the evening in the casino, gambling. We do not know what games he was playing, but we do know he wasn't paying much attention to his daughter. Twice casino officials led her back to her father. But Sherrice was having fun, playing in the casino's video arcade, amusing herself.

Also in the casino were David Cash snr, holidaying with his son, David, and his son's best friend, Jeremy Strohmeyer, both aged 18. They were star maths students at a Long Beach high school.

Some time after 3 a.m. Strohmeyer and Sherrice began playing a game, tossing wet paper towels at each other. If anyone saw them, nothing seemed amiss.

At 3:47 a.m. a video surveillance showed Sherrice running into a women's toilet, chased by Strohmeyer. David Cash followed. Strohmeyer chased Sherrice into a stall and put his hand over her mouth. David Cash peered over the stall and, according to him, said to leave the little girl alone.

Strohmeyer began taking off Sherrice's clothes and assaulting her. Cash left the room after two minutes and stood outside.

Strohmeyer emerged 24 minutes later and said he had raped and strangled Sherrice to death. By his own recollection, David Cash's only response was to ask Strohmeyer whether Sherrice had become sexually aroused. When a stunned Los Angeles Times reporter asked Mr Cash how he could possibly have wondered if a seven-year-old girl was aroused, he said: "That's just the way I think".

Back in Long Beach, the two returned to school. When police released the video surveillance tape, their classmates recognised them on television. Strohmeyer was arrested and David Cash agreed to testify. But Mr Cash was never charged with a crime. In Nevada, as in many states, he did nothing illegal.

"There is no law requiring citizens to report a crime and no law requiring them to stop a crime," said Sgt Kevin Manning of the Las Vegas police. "There is a moral obligation, but we don't arrest people on moral issues."

Nonetheless, the Woodrow Wilson High School was not pleased with its now-famous students. With Strohmeyer in jail awaiting trial, they expelled Mr Cash and forbade him from attending graduation ceremonies. Brazen, he showed up anyway, waving to television cameras from a white limousine and going to a friend's house to watch himself on the TV news.

Then, as he was about to start a nuclear engineering course at Berkeley, David Cash began to talk, on radio and television shows.

He told the Los Angeles Times: "I'm not going to get upset over somebody's else's life. I just worry about myself first." He told the CBS television show 60 Minutes: "I don't feel there is much I could have done differently". He also had no remorse about not seeking help during the attack. "I didn't want to be the one to turn him in . . . He's also my best friend."

Then Mr Cash told a radio callin show that his notoriety was helping him to "score with women". He also said he did not know Sherrice Iverson so he could only feel bad about his friend, Jeremy.

Students at Berkeley had enough (their last famous maths genius was a professor named Ted Kacinski, the Unabomber). They have held protests demanding Mr Cash's expulsion. Twice the student body has passed resolutions asking Cash to leave, but its president, Irami Osei-Frimpong, has vetoed them. "I do not believe it's the organisation's right to cast moral judgments without benefits of due process."

Similarly, the university chancellor says the school has no grounds to expel Mr Cash. He has committed no crime and violated no school rules.

As Strohmeyer and Mr Cash were white, and Sherrice Iverson was black, the case has ignited allegations of race discrimination. Many lawyers contend that black youth are routinely charged just for being at the scene of a crime.

Last week Strohmeyer was convicted of murder and sent to jail for life. In a rambling diatribe in court he blamed a variety of people for the crime, his adoptive parents, the America Online Internet service provider that first allowed him to see pornography, the Nevada Gaming Commission which did little to patrol the casino, and he finally blamed Mr Cash, "an unfeeling hater . . . who would not lift a finger to save an innocent child from the drunken, drugged-out mess that I was".

That speech did little for Yolanda Manuel, Sherrice's mother. She has no time for Strohmeyer, and no time for Mr Cash's promising nuclear engineering career. She wants him out of college, even if he cannot be charged.

"My baby won't ever get to college," Mrs Manuel said. "David Cash shouldn't be able to get on with his life like nothing happened. I sure can't."