Santa Clara County DA wants to know if rail yard shooting could have been prevented

Could the VTA shooting that claimed nine lives, have been prevented?

That's what Santa Clara County District Attorney Jeff Rosen wants to know.

He's demanding access to a 2016 report, outlining an encounter between Customs and Border Protection and the shooter, Sam Cassidy.

"Once I read that report I've indicated that I want to talk with the head of Customs and Border Protection in the Bay Area to try to understand why that information was not shared with local law enforcement at the time," says Rosen.

Allegedly found in Cassidy's possession, books about terrorism and notes outlining his hatred for the VTA.

Rosen says had local agencies been alerted, they could have investigated and intervened.

"They may very well have talked to friends or neighbors or coworkers, talked to Mr. Cassidy, ascertained whether he had any weapons, tried to get a sense of what his mental state was," says Rosen.

Experts say while hindsight is 20/20, the decision whether to pass on that information might not have been clear cut at the time.

"Nobody wants to be the one who says you know what, I should have passed this along," says Jerry Robinette, who used to run Homeland Security Investigations for Immigration and Customs Enforcement in Texas and now works for law firm, Nixon Peabody.

He says it's routine for federal agencies to share information with locals: everything from obvious threats to hunches.

"The roadblocks that people envision are not there. I mean we work together too often on a regular basis," he says.

Rosen wants to make sure that's the case moving forward.

He says, he was there in the hours after the VTA shooting, when the victims families were notified.

"And I heard the cries and the screams and I saw people throwing up. And those are images that I will never forget," Rosen says.

And he says while Cassidy alone is to blame for this tragedy, it's time officials ask themselves some hard questions: "What could we have done differently and better to prevent this? What can we do going forward to minimize the chance of this happening again?"

Customs and Border Protection did not respond to our request for comment. Rosen believes he'll be getting a copy of that 2016 report in the coming days.