It is argued, that content analysis methods, such as Statement Validity Assessment, Reality Monitoring, and Scientific Content Analysis are not accurate enough to be admitted as expert scientific evidence in criminal courts. A new assessment procedure – Multi­variable Adults’ Statement Assessment Method (MASAM) was proposed. MASAM assumes, that the Undeutsch hypothesis should be followed by supplementary assumptions: every testimony contains both truthful and falsified accounts; validity of the adults’ statements may not be assessed in general; the process of eyewitness testimony formation must be taken into consideration to form the final opinion about veracity of the statement. Study conducted on group of twelve forensic psychologists (of which 6 used SVA, RM or SCAN, and 6 MASAM assumptions), assessing 30 statements (15 truthful, and 15 fabricated) has proven, that MASAM enables more accurate veracity assessment. It was found, that concordance coefficient is significantly higher when MASAM is applied.