Modern methods in warfare make it difficult to attribute responsibility for war crimes. The paper examines that in three instances: private military and security companies (PMSCs), lethal autonomous robots (LARs) and computer network attacks (CNAs). With PMSCs the crucial question is whether the hiring contract proves a sufficient link to engage the hiring state's responsibility for the company's misconduct. Since LARs are not operated by a human, the options for assigning individual criminal responsibility are doubtful. CNAs suffer from the as yet unsure technical means to definitely establishing their source. Although CNSs targeting a civilian object are likely war crimes, the technical impossibility of establishing the source prevents the verification of either state or individual responsibility.