What characteristics do scientists use to distinguish between organisms in different kingdoms

Similarities and dissimilarities between the organisms - similar featured organisms will be kept in one group and dissimilar featured organisms in other group. Different features like no. of cells, nature of body surface, nature of body cavity nature of skeleton, nature of locomotion, nature of sexual parts, nature of circulatory system etc.

They are like other investigations? say there was a murder u have to do blood test and finger prints which run through a lab.