In recent years,low copy number biological evidence,which has been brought into generous focus,plays an increasingly important role in forensic DNA analysis.Meanwhile,great pace has been made in the development of testing methods used for low copy number DNA.By summarizing a variety of LCN-DNA analysis techniques like increasing the number of amplification cycle,PCR products purification,whole genome amplification,laser microdissection and by evaluating the LCN-DNA testing results,the paper is written to illustrate comprehensively and thoroughly the latest advancement and existing problems in it application and the existence problems in forensic science,so as to develop its application in criminal justice into the fullest play.

Objective To analyze the 2496 biological samples collected from 1574 larceny cases and improve the application of DNA in the larceny cases. Methods Make a summary of the biological samples collection methods and DNA test results in different type of larceny cases. Results Touch samples have already become the most common type of biological samples in larceny cases, but their DNA test success rate are still low, more work should be done for the DNA mixed type to improve DNA hit. The DNA positive result rate had statistical difference in biological samples with different collection methods. For the Touch samples, flocked swab and original are the best collection methods. Conclusion More Valuable biological samples collected by the crime scene investigators are the Key factor in improvement of DNA detection capability, awareness of trace biological evidence and the touch sample collection technique are very important for the crime scene investigators.