In many cases, legal psychological expertise includes the evaluation of the cognitive state of a person. In particular, that relates to the cognitive impairment due to dementia. Alzheimer's disease (AD) is the most common form of dementia. There are multiple biomarkers and neurological diagnostic procedures, however, they are often not applicable in the legal context. Handwriting analysis is a potential method for early detection of the onset of the disease. It allows the investigation of current specimens as well as documents from the past, which is especially important for forensic. In the article we present an instrument for screening of possible AD (AD-HS) by handwriting. It includes 40 handwriting and 2 linguistic markers. Their cumulative assessment allows the evaluation of a quantitative AD Indicator (ADI), which reflects the severity level of impairment. The presented validation study includes 48 persons with the AD diagnosis and the control group of 182 handwriting specimens from the database of the HSDetect system for handwriting analysis. The mean value for ADI in the control group equals 0.26 and the 95% level lies at 0.46. All participants have higher ADI value with an average value of 0.46. Besides, the correlation between ADI and the severity of AD was 0.64. That is, AD-HS allows the evaluation of AD severity. The presented approach provides a practical instrument for forensics and criminal expertise. Further refinement of AD-HS and the extension of the experiment data will allow even more reliable screening of cognitive impairment through handwriting. Keywords: forensic psychological examination, Alzheimer's disease, indicator of Alzheimer's disease, cognitive impairment in handwriting, dementia.