Did she realise she had killed the cats? Does seem odd, two cats at once, my cat lazes about in the middle of our very quiet road, but dashes off when a car appears. Sorry about losing your cats, but I think you need to be absolutely sure about what actually happened, the laughing may have been at what someone had just said, or something she heard on the radio. It is a serious accusation and one you need to be certain of; maybe speak to the clients she visits and get the name of the agency that employs their carer and call them, but when you are calm and collected. Hysterical accusations and death threats will not get you any sympathy or make her employers willing to deal with this in the proper way. Sorry about your cats 