"I have to say what I see. I have to be true to what I believe," he said.
For the first time as chief, he was urging the D.A. to consider criminal charges against one of his own officers for the fatal shooting of Brendon Glenn.
Glenn's autopsy was released on Monday, and it showed the 29-year-old had been high on alcohol and marijuana the day of the shooting last May.
A security camera recorded what started as a scuffle. Investigators who have seen the video said the officer, Clifford Proctor, did not have to shoot.
Proctor's lawyer told Eyewitness News that that the camera angle is misleading.
"You are not looking at it from Proctor's point of view. Proctor saw this guy go for his partner's gun," he said
Beck, however, did not agree.
"I will say the evidence does not support that," he said.
Los Angeles police are keeping that video under wraps because the chief said releasing it now could damage the investigation.
"It will be used to test the veracity of witnesses," he said. "Its release could taint a potential jury pool."
The review from activists who are typically critical of the LAPD said Beck has done the right thing.
"We think it is just as important to commend Chief Beck when we feel he is doing something right," said Najee Ali of the National Action Network.
As for the D.A., there was no word on how long it will take to determine if criminal charges should be filed.