A man who spent 19 years in jail for the murder of two children will be exonerated formally in July, putting the number of inmates in America cleared by DNA evidence at more than 200.

Byron Halsey, who narrowly avoided the death penalty when he was convicted in 1988 of the sexual assault and murder of a girl, 7, and a boy, 8, had his conviction thrown out by a judge last week after DNA evidence pointed to another man as the killer.

Mr Halsey’s exoneration means that since the first American inmate was cleared by DNA evidence in 1989 another 200 have now been proven to be convicted wrongfully, according to the Innocence Project, a New York legal charity that pioneered the use of DNA analysis.

Of the 201 now exonerated, 120 were black and 15 had spent time on death row. Together, they had served 2,496 years.

One of the most striking statistics from the cases, which demonstrates a distinct bias against African-American men, involves sexual assaults.

Nationally, only 12 per cent of sexual assaults are between a victim of one race and an attacker of another – yet 64 per cent of those exonerated were black men convicted of raping white women.

In the cases, 28 per cent were convicted of murder. Overall, three quarters were the result of inaccurate identifications at police lineups.

Remarkably, a quarter of those now proved innocent confessed, and 4 per cent pleaded guilty.

Among the people freed are Jerry Frank Townsend, who served more than 21 years in a Florida prison for six murders and a rape.

Mr Townsend, who has the mental capacity of an eight-year-old, confessed to multiple crimes. After 20 years in jail, the mother of one of the victims convinced police to review the case. DNA testing cleared Townsend and implicated another man, already in prison on other rape and murder charges.

In another case, Frank Lee Smith was on death row for the rape and murder of an eight-year-old girl. He died of cancer in 2000 before being exonerated officially.

The first US inmate to be cleared by DNA evidence was David Vasquez, a janitor of below-par intelligence who confessed to the 1984 rape and murder of a young woman in Virginia. Sentenced to 35 years, he had spent five years in prison before DNA testing – then a new science – cleared him. He was pardoned formally in January 1989.

Since then, convictions have been quashed thanks to DNA evidence in 31 states. In 43 cases the real assailant was eventually found. But the Innocence Project calls the 201 cases just the “tip of the iceberg”.

Only 10 per cent of crimes leave biological evidence that can be tested for DNA. Maddy Delone, the executive director, told The Times that the organisation now has another 250 cases and is processing requests from thousands of others.

“We can’t know exactly how many wrongful convictions there are,” she said.

But she cited a random sample of 29 sexual assault convictions reexamined recently by authorities in Virginia. Two men were found to be innocent.

In another study this year, of 319 rape/murder convictions between 1982 and 1989 where DNA evidence exists, 11 men were found to be innocent.

DNA testing has led to widespread reforms, such as a national DNA database, the video-taping of interrogations and changes in line-up procedures, where victims were often “encouraged” by police when looking at a particular suspect.

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