12 Then the chief priests, the teachers of the law and the elders looked for a way to arrest him because they knew he had spoken the parable against them. But they were afraid of the crowd; so they left him and went away.

Read Mark 12:12 Using Other Translations

And they sought to lay hold on him, but feared the people: for they knew that he had spoken the parable against them: and they left him, and went their way.
And they were seeking to arrest him but feared the people, for they perceived that he had told the parable against them. So they left him and went away.
The religious leaders wanted to arrest Jesus because they realized he was telling the story against them—they were the wicked farmers. But they were afraid of the crowd, so they left him and went away.