Impeachment metaphor:

The police come to see you, they have extremely convincing evidence that your brother brutally raped a woman and then murdered her to cover up his crime. But you decide to provide them with an airtight alibi for your bro. You lie and tell them you had spent the entire night of the crime playing chess at your house with him; there is no way he could have been at the scene of the crime. You also manage to convince your wife and kids to back up your story.

After all, he IS your brother. You love him, and besides, he's just offered you a really good job in his company.