You can care about someone and still refuse to be the alibi in their story.

Loyalty gets stretched into covering, and the stretching happens gradually, one small thing at a time. Caring about somebody does not require you to hold their version of events or absorb the cost of what they did. You can stay close to a person without standing behind a story you do not believe.

If you are being asked to confirm something you are not comfortable with, refuse that specific thing rather than the friendship. Keep it narrow: I cannot say that. You can still be there for them afterwards, and the refusal usually matters less to them than you fear.