The Criminal Justice System heavily relies on eyewitness testimony (EWT) during legal proceedings because many crime scenes are lacking DNA traces. However, human memory is susceptible to errors, biases, and forgetting, which also make it easy to imply false memories. A lack of knowledge regarding what can influence witness memory might result in wrongful convictions and even the death penalty. The aim of this article was to critically evaluate the reliability of EWT by referencing empirical research regarding system and estimator variables, such as; trauma, weapon focus effect, intelligence, alcohol, age, and post-event information. The results of some studies have shown that under certain circumstances, the effects of some of the variables have not been observed. On the other hand, there is strong evidence that the testimony of elderly witnesses does not make a reliable form of evidence. The same applies to alcohol intoxication and its negative impact on memory. The conclusion emphasizes the importance of knowledge about what affects witness testimony in the legal system. It states that even if some results claim that no negative effects were found, the CJS should not be completely certain about eyewitnesses’ testimonies. In addition, besides the context of the witnesses, the essay highlights how unreliable our memory can be.