Gabriel Morales, 25, resigned in September when internal affairs investigators searched his home. They reportedly found information on two witnesses in the murder trial of 18-year-old Matthew Turner.
"The trust of the community, the trust of the residents of this city is paramount to the Los Angeles Police Department," said Beck Monday. "When someone violates that trust, they can no longer be a Los Angeles police officer."
Beck said if Morales had not resigned, he would have been fired.
The L.A. District Attorney's office will decide whether to file criminal charges against Morales.
City News Service contributed to this report.