Recently, the importance of vehicle speed analysis from video images in traffic accidents and incidents has been increasing, and with the development of camera technology, there is an urgent need to improve image analysis technology. Among the influencing factors, the complexity of the frame rate due to digitization of video signals, and the time difference of imaging within the same frame due to the rolling shutter method of CMOS cameras are thought to influence the accuracy of vehicle speed analysis.

Therefore, we developed a software that can automatically read frame rates down to 1 ms by analyzing video images of a device (Time Counter) with a stopwatch function using LEDs. This software automatically read frame rates by cropping the frames, correcting lens distortion, generating orthogonal images through homographic transformation, and binarization of the images, then reading the coordinates of the lit LED points. Next, we developed a scanning time measurement device. This is a device that blinks an LED tape light at an arbitrary frequency. When this device is shot by a CMOS camera with rolling shutter method, the LED tape light is imaged in stripe pattern. The scanning speed can be measured by measuring the width of the stripe.

Moreover, we proposed a vehicle speed analysis method that takes scanning time into account, and conducted physical experiments to confirm its effectiveness．As a result, the proposed method achieved an error of ± 0.1 km/h, while the conventional method showed an error ranging from ‒1.48 km/h to +1.46 km/h. The proposed method improved the accuracy of vehicle speed analysis.

Colorimetric tests are effective as rapid and simple methods for criminal investigations. Given the recent increase in cannabis-related crime, cannabis detection methods have received significant attention. The widely used Duquenois-Levene (D-L) method, however is known to produce false-positive results, highlighting the need for alternative methods. The 4-aminophenol based method has been proposed as a promising substitute due to its ability to discriminate Δ⁹-THC and CBD. However, it has a critical limitation: it is inapplicable to mixtures of Δ⁹-THC and CBD. In this study, we introduced a phase separation technique using an organic and aqueous layer, inspired by the D-L method, into the 4-aminophenol based method. This modification enabled the separation and identification of Δ⁹-THC and CBD in mixed samples. Furthermore, under the same conditions, the separation of Δ⁹-THC and Δ⁹-THCA was also achieved. Based on this newly developed method, we designed the rapid test kit that offers both ease of use and enhanced specificity. By establishing a positive detection criterion that requires the presence of both Δ⁹-THC and Δ⁹-THCA, the test kit significantly reduces false-positive results compared to conventional methods. These advantages make it a promising candidate for practical application in forensic field investigations.

Toxicological hair analysis has become an indispensable technique for investigating crimes such as drug abuse and sexual assault. However, due to the inherent difficulties of trace analysis and the unique characteristics of hair as a matrix that differ from those of other biological samples, hair analysis has not yet been fully integrated into the practice of forensic toxicology in Japan.

In this paper, we aim to encourage the wider adoption of hair drug analysis in Japan’s analytical laboratories. We will focus on practical knowledge and techniques, particularly sample preparation methods, and present the results of our group’s 20-year research and development in toxicological hair analysis.

In this study, we investigated the stability of reagents and improvements to the kit. Regarding improvements to the kit, we were able to develop a kit that is more suitable for on-site use by using a plate with a concentration zone and a spreading chamber.

To examine stability, Fast Blue BB (FBBB) was dissolved in chloroform and stored at room temperature under light-shielded and non-light-shielded conditions, and TLC was performed after 2, 7, 14, 21, and 28 days. As a result, although it could be used for up to 2 days after storage without light shielding, normal color development was not observed after 7 days, and even when TLC was performed, no Δ⁹-THC spots could be confirmed. On the other hand, for those stored in the dark, a normal color reaction was observed even 28 days after preparation, and a spot could be observed in the same position as the standard solution on TLC.

After the standard solutions were prepared, they were stored for 7, 14, and 28 days under four storage conditions (room temperature, shielded from light, drying, and shielded from light + drying). When TLC was performed for each storage condition, it was confirmed that all the products could be used for the specified period of time without any problems.

Age estimation based on DNA methylation rates can provide useful information on unknown suspects and victims of crimes from biological materials like blood. We have previously shown the accuracy and effectiveness of the age estimation methods using a pyrosequencing approach on Japanese blood and aged bloodstain samples. However, the DNA quality required for an accurate age estimation is not known: effects of DNA degradation on the methylation rate-based age estimation methods are not clear. In the present study, we evaluated the effect of DNA degradation on the three age estimation methods by using artificially degraded DNA samples. When we used a default amount (50 ng) of DNA for age estimation, enzymatically degraded samples ranging 1.12–4.54 in the degradation index by Quantifiler^TM HP DNA Quantification Kit predicted age accurately with a comparable level to undegraded DNA. On the other hand, in case of using a less amount (<50 ng) of DNA, degraded samples caused an unignorable level of difference in the methylation rates of ELOVL2 markers and age predictions by the three estimation models between undegraded control DNA. These results indicate the importance of using a sufficient DNA to ensure an accurate age estimation on forensic samples.

DNA degradation or low DNA quantity (e.g., in the case of DNA extracted from bone samples) is likely to decrease the number of loci detected in short tandem repeat (STR) typing. In this study, we evaluated the effect of the decreased number of loci on full sibling analysis through the likelihood ratio (LR) calculation. Simulations were performed by decreasing the number of loci using the previously studied data for full siblings (10,000 full sibling pairs and 10,000 unrelated pairs) that had been generated for the 21 autosomal STR loci in the GlobalFiler kit using the allele frequencies of the Japanese population. For each pair, we excluded the loci one by one in order of longer to shorter fragment size (fragment size model, assuming DNA degradation) or randomly (random model, assuming low-template DNA) from the LR calculation. As a result, the effect of decreased locus number in the fragment size model was slightly larger than that in the random model. Although decrease in the number of loci used in the LR calculation reduced the distance between the LR distribution in full sibling pairs and that in unrelated pairs, it was shown that even if the number of loci decreased, this does not immediately eliminate the usefulness of the LR for full sibling analysis.