Turn over a rock - Tradução em português

Olá pessoal!

Minha dúvida é relativa à expressão "Turn over a rock" (acho que não tem o sentido literal...) num texto que estou traduzindo. Aí vai o contexto completo:

When an officer went to the home to follow up, he spoke with Garrido in the front yard, warning him there were restrictions against living outside in a residential neighborhood, Rupf said.

"He did not enter, nor request to enter the backyard," Rupf told reporters, adding that the officer did not know that Garrido was a registered sex offender, even though he is listed as such on a public database.

"This is not an acceptable outcome," Rupf added. "Organizationally we should have been more inquisitive or curious and turned over a rock or two."

Obrigado desde já!