Judge James Donato is overseeing Epic v. Google, a case that could determine the future of the Android app store — but testimony in this case may have more repercussions for Google too.

On Friday, Judge Donato vowed to investigate Google for intentionally and systematically suppressing evidence, calling the company’s conduct “a frontal assault on the fair administration of justice.” We were there in the courtroom for his explanation.

“I am going to get to the bottom of who is responsible,” he said, saying he would pursue these issues “on my own, outside of this trial.”

Testimony in the Epic v. Google trial — and in a parallel DOJ antitrust suit against Google in Washington, DC — revealed that Google automatically deleted chat messages between employees, and that employees all the way up to CEO Sundar Pichai intentionally used that to make certain conversations disappear. Pichai, and many other employees, also testified they did not change the auto-delete setting even after they were made aware of their legal obligation to preserve evidence.

And Pichai, among other employees, admitted that they marked documents as legally privileged just to keep them out of other people’s hands.

On November 14th, Pichai told the court that he relied on his legal and compliance teams to instruct him properly, particularly Alphabet chief legal officer Kent Walker — and so Judge Donato hauled Walker into court two days later.

But the judge was not satisfied with Walker’s testimony, either, accusing him of “tap-dancing around.”

Walker said he never attempted to audit whether employees were actually retaining evidence — it was left up to individual employees to decide which communications might be relevant to a legal case, and more than one employee testified in court they had the wrong idea of what was relevant.

Today, Judge Donato said it was “deeply troubling to me as a judicial officer of the United States” that Google acted this way, calling it “the most serious and disturbing evidence I have ever seen in my decade on the bench with respect to a party intentionally suppressing relevant evidence.”

“This conduct is a frontal assault on the fair administration of justice. It undercuts due process. It calls into question just resolution of legal disputes. It is antithetical to our system,” said Judge Donato.

And yet, the judge decided today that he would not issue a “mandatory inference instruction” — one that would tell the jury they should proceed with the understanding that Google destroyed evidence that could have been detrimental to its case.

Instead, there will be a “permissive” jury instruction — the jury “may” infer that the missing evidence might have helped Epic and hurt Google.

“The best course of action is for the jury itself to decide whether it will make an inference. I am not going to constrain the jury’s discretion by making that inference for them,” he said.

“Even though it would be well within bounds to issue a mandatory inference instruction,” said Judge Donato, “I can pursue these issues on my own, outside of this trial, in subsequent trials.”

“I am going to get to the bottom of who is responsible,” he said. “That is going to be separate and apart from anything that happens here, but that day is coming.”

Google declined to comment to The Verge on Judge Donato’s statements.

Today, Epic and Google rested their case in Epic v. Google. We’ll be returning on December 11th for closing arguments and jury instructions.