Species that murder their own counterparts when put in captivity
Some individuals kill their own offspring (https://en.wikipedia.org/wiki/Infanticide) or eat their offspring (https://en.wikipedia.org/wiki/Filial_cannibalism) or their own siblings (https://en.wikipedia.org/wiki/Siblicide).  See this article about siblicide and fratricide in bacteria:  https://www.webmedcentral.com/article_view/4804.  

Other conflict and killing between members of a population occurs in many species, including humans (https://en.wikipedia.org/wiki/Homicide), mice (https://sci-hub.tw/10.1111/j.1469-185X.1991.tb01147.x), and other primates (https://www.sciencedirect.com/science/article/pii/S0140175082920632).  

Search "intraspecific killing" on Google or Google Scholar.    

See also a similar question here:  Why social animals attack odd members of their own group?