Keith Boyer, a police officer in Whittier, California, was shot and killed earlier this week. The killer is believed to be Michael Christopher Mejia.

According to the Los Angeles Times, Mejia is “a career criminal with a history of drugs and violence.” He has “cycled in and out of jail for repeatedly violating the terms of his release.”

Here are the details:

Court records show that Mejia was sentenced in 2010 to four years in state prison for robbery and was convicted in July 2014 of grand theft auto and attempting to steal a vehicle. He was given another two-year sentence. . . . [He] has been arrested and jailed for short stints several times since July. State officials said he was on probation and under supervision of the L.A. County Probation Department. In July, he violated terms of his release and got 10 days in jail. He was arrested again in September after authorities moved to revoke his community supervision. He was arrested in January [last month] for again violating the terms of his release and sentenced to a combined 40 days in jail. But he was out again after 10 days, records show. Then, Feb. 2 [this month] he was arrested by East L.A. sheriff’s deputies for violating his release terms and “flash incarcerated.”

How is it that Mejia kept getting out of jail? Bill Otis quotes the Los Angeles County sheriff, who points to three measures enacted in the last seven years — Propositions 47 and 57 [see update] and Assembly Bill 109 — that have led to the release of too many criminals without creating a proper safety net of mental health, drug rehabilitation and other services.

Ed Whelan points to the Supreme Court ruling, by a 5-4 vote, to which the aforementioned Assembly Bill 109 was a response. That ruling required California to release the staggering number of 46,000 convicted criminals and to maintain its prison population below a certain threshold.

California prison officials deny a causal relationship between that decision and Mejia’s releases from prison. They say the decision “did not impact time served” by Mejia, but only “the entity handling supervision of [him] following [his] release.”

Even if this is true, and I don’t know whether it is, the entity that supervised Mejia after his release clearly did not supervise him properly. With proper supervision, it’s difficult to see how a chronic offender, who violated the terms of his release last month and this month, would be on the street.

One way or another, Officer Boyer appears to be the victim of sentencing reform, whether by judicial fiat, misguided laws, or the two in tandem.

We’ve pointed out repeatedly that America has an under-incarceration problem. Sensible sentencing reform would be dedicated to keeping criminals like Christopher Michael Mejia locked up, not to letting them out of jail.

I agree with Whittier police chief Jeff Piper:

We need to wake up. Enough is enough. This is a senseless, senseless tragedy that did not need to be.

It would not have happened absent the tragically misguided sentencing reform impulse.

UDPATE: The California Department of Corrections and Rehabilitation informs me that Prop. 57 has not yet been implemented. It was passed by voters last November, but requires regulations for its implementation. Those regulations are in the process of being developed.