(Reuters) - A California inmate sentenced to death 28 years ago died in hospice care this week, the state said Monday, bringing the total of condemned inmates who passed away from natural causes to 68 in a state that has not carried out an execution in years.

The death of Teofilo Medina, Jr., 70, at a medical facility near Sacramento comes amid ongoing controversy in California over how the death penalty is administered, including a recent decision by a federal judge declaring the state's use of capital punishment unconstitutional, because inmates lingered on death row for years or even decades.

"This is just another wake-up call to say that California's death penalty system doesn't work," said Ellen Kreitzberg, a death penalty expert at Santa Clara Law school near San Jose. "It doesn't contribute to any legitimate purpose for punishment."

Medina had been on death row since 1987 for a California robbing and killing spree that began shortly after he was released from an Arizona prison on a rape conviction. He was the second death row inmate to die of natural causes this month, the state said.

The death penalty was voided in numerous states, including California, by the U.S. Supreme Court in 1972, but many soon adopted sentencing reforms that met the high court's requirements. Among them was California, which reinstated its death penalty in 1978.

But a lengthy appeals process, along with a lack of political pressure to carry out executions, has left California with 751 people on death row. Since the penalty was reinstated, 13 inmates have been executed, 23 have committed suicide and 68 have died of natural causes, the state said Monday. One was executed in Missouri.

The state has not put an inmate to death since 2006.

In 2012, a ballot measure to abolish the death penalty lost narrowly, garnering 47 percent of the vote.

Last year, a Field Poll showed support for capital punishment at a 50-year low in California, with 54 percent of voters supporting the death penalty, down from 68 percent in 2011.

Opposition to the death penalty has also grown amid concerns that the drugs used for lethal injections have led to botched executions and painful deaths.

The exoneration of some inmates by the Innocence Project and other legal activists has also prompted new skepticism.

The state announced Medina's death, but did not immediately comment on his lengthy stay on death row.

(Reporting by Sharon Bernstein; Editing by Sandra Maler)