The phrase "bloody knife" refers to a knife that has blood on it. It typically indicates that the knife has been used to harm someone and is often associated with violence or a crime. Full definition
From the opening scene of young psycho - in - the - making Michael Myers greeting his parents with bloodied knife in hand to his inevitable return to wreak more havoc a decade later, Halloween ticks every box. (timeout.com)
With huge bloody knifes on their roofs and pastors with keffiyeh headdresses bound with agal, (nakedpastor.com)
The technology matured in the academic community, and if used properly, makes it possible to link an individual to evidence such as bloody knives or semen - stained clothing. (cen.acs.org)