Once criticized as a sham, BART’s cameras played a key role in identifying John Lee Cowell, the parolee who allegedly stabbed to death a young woman Sunday night on the MacArthur BART Station platform in Oakland.

And, from the looks of it, the cameras also showed other key details certain to be useful to prosecutors at trial.

It was only last year that BART finished installing live digital cameras aboard all trains after The Chronicle revealed that three-fourths of the cars had only decoys — camera shells that were meant to discourage crime but didn’t actually function.

This time, BART was able to record Cowell, a transient on parole for robbery, from the time he got on the train until after the attack.

But it was the platform cameras — and those inside the nearby MacArthur parking structure — that also provided the key evidence about what happened.

According to BART spokeswoman Alicia Trost, video aboard the train shows that when victim Nia Wilson, 18, and her older sister, 26-year-old Lahtifa Wilson, boarded the rail car in Concord, they had no contact with Cowell.

In other words, there wasn’t any sign of conflict prior to the attack.

It was only as the two women got off at MacArthur to change trains that Cowell allegedly swooped past them, fatally slashing Nia Wilson in the throat and wounding her sister. That horror was captured on station cameras and helped police identify Cowell.

BART cameras inside the station’s parking garage showed Cowell removing his jacket and pants afterward, apparently changing his clothes.

“This is key to showing him knowing what he was doing, and that he was not out of his mind,” Trost said.

As it turns out, BART police got Cowell’s name from “identifiable information” he left at the scene — which they matched to a fare-evasion citation he had received just days earlier, on July 18. More importantly, Cowell’s face had been captured on a BART police officer’s chest camera during that stop — providing authorities with a high-quality photo of the suspect that was released to the public.

The new cameras come at a key time for BART, as concerns among riders continue to grow about the system’s safety and its police force remains 25 officers short of its budgeted staffing level.

“I totally understand the concerns that folks have,” BART police Chief Carlos Rojas told reporters Monday.

But Rojas also noted that BART is not alone when it comes to public safety challenges.

The same type of crimes that are found on the streets of San Francisco, Oakland, Hayward, Concord or any of the other cities that BART serves are now “bleeding into our stations,” he said.

BART has 227 sworn officers, putting it ahead of both Fremont and Santa Clara — with 199 and 155 officers respectively. Those two Bay Area cities’ 200,000-plus populations roughly equal the number of BART’s weekday riders, but there is an important difference.

BART’s officers have to cover trains filled with passengers traveling over 121 miles of track spread over three counties and 48 different stations.

“In general, there is one officer to every two to three stations” on patrol, Rojas said.

But it’s possible to have cameras everywhere — which may explain why, just last week, the Bay Area’s congressional delegation led by Eric Swalwell, D-Dublin, wrote a letter to Homeland Security Secretary Kirstjen Nielsen backing BART’s request for another $11.2 million for cameras and other security upgrades.

In the trees: All attention at the Bohemian Club’s annual redwood forest retreat in Sonoma County on Friday was on Camel’s Camp, where retiring Supreme Court Justice Anthony Kennedy took center stage.

Kennedy used the Bohemian Grove appearance to talk about both the history and future of the high court. And the response from the largely conservative group of 150 campers was rather tepid, we’re told.

“There was polite applause, but a lot of people didn’t clap,” said a club insider privy to the exchange. “There was a lot of talk that Kennedy sold out,” allegedly having agreed to retire from the bench in exchange for President Trump’s picking his conservative former law clerk Brett Kavanaugh to succeed him.

In contrast, over at the Owl’s Nest encampment, we’re told TV pundits Chris Matthews, David Gergen and David Brooks lit up the crowd, especially when Brooks lamented the “loss of honesty, truth and civility” during the Trump era, calling it a “disaster and threat to democracy.”

“The entire camp erupted into applause,” says our spy.

San Francisco Chronicle columnists Phillip Matier and Andrew Ross appear Sundays, Mondays and Wednesdays. Matier can be seen on the KPIX TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call 415-777-8815, or email matierandross@ sfchronicle.com. Twitter: @matierandross