A man on death row has been killed by a fellow inmate, the first murder of its kind in California in more than 20 years.

Jonathan Fajardo was stabbed in the neck and chest in a recreational yard on Friday. He died about half an hour later.

He had been in an exercise yard at San Quentin State Prison, about 17 miles north of San Francisco.

Corrections department spokeswoman Terry Thornton named the suspect as Luis Rodriguez, 34, also a condemned inmate.

Rodriguez's alleged motive is not known and it is not clear how he was able to get the weapon, described by the corrections department as "inmate-made".


Image: Luis Rodriguez is accused of murdering his fellow death row inmate

Fajardo, 30, was a gang member awaiting execution for two murders: a 14-year-old black girl killed in a racially motivated shooting, and a man stabbed because gang members believed he might be helping police.

He had been on death row since 2011.

Rodriguez was given a life sentence for murder in 2008 but seven years later he was sentenced to death for the murders of two rival gang members.

Image: An armed guard patrols on the east block for condemned prisoners at San Quentin State Prison

Despite inmates being on death row for the most violent of crimes, that part of the prison usually has the lowest levels of violence, according to Amy Smith, an associate professor at San Francisco State University who studies capital punishment and the psychological impacts of death row.

There is high security and most inmates have their own cells, but many of them are allowed to gather in the exercise yard - where Fajardo was killed.

She said the murder was "very unusual, it's not supposed to happen, of course".

The last time there was a murder on death row in California was in 1997.

Since 1978, when California reinstated capital punishment, 78 condemned inmates have died from natural causes, 25 have killed themselves, 13 have been executed in California, one was executed in Missouri, one was executed in Virginia, and 10 died from other causes.

There are 742 offenders on California's death row but there have been no executions in the state since 2006.