Picture this scenario

Imagine you're at work and a colleague suddenly begins acting weird. She's all stiff and staring into space and distant, and not doing her usual tasks. After a couple of days she explains she's not the person you knew, she's a robot or alien and said she killed your colleague to take her form, but she's sorry, but she's here to help against an alien attack.

Do you say it's ok that she killed your colleague and you're glad she's helping or do you try to get away from her not wanting to discover if she'd kill you too?

The colleague btw was not someone you hated?

"Hi, I saved earth. Had to kill your friend/sister/mother/wife/gf/niece/aunt etc to do so, sorry about that, but I needed to have a functioning recognisable image to avatar myself instead of just explaining I'm not a threat to you. Hope we can be friends?"