NEW DELHI, Oct. 24 -- Delhi Police conducted two rare tests of forensic DNA profiling to establish the alleged involvement of four accused in the gang-rape and murder of a 16-year-old girl in outer Delhi's Swaroop Nagar, with a Central Forensic Science Laboratory (CFSL) report confirming the presence of "human semen" and "a mixed male DNA profile corresponding to four males on swabs collected from the victim", officers aware of the findings said on Thursday. Police said that the body of the girl was highly decomposed and these scientific tests were essential to link the victim to the accused. "They are essential when the DNA is possibly contaminated and when there is a possibility of multiple DNAs. Hence, the exhibits were sent to Central FSL in Chandigarh," the officer said. A police officer aware of the matter said that the report found that the Y-chromosome short tandem repeat (Y-STR) profiles of all the four accused strongly matched the mixed male mitochondrial DNA profile recovered from the victim's swabs, corroborating the allegations of sexual assault. "The CFSL report has been received. It confirms the presence of human semen on the victim's swabs and a mixed DNA profile corresponding to four different males. The Y-STR profiles of all the accused show a strong match with the male DNA recovered from the victim. The findings support the investigation and corroborate the involvement of the accused," the officer said. A FSL official explained that Y-STR analysis examines genetic markers on the Y chromosome, which is passed down the paternal line. The technique is useful in sexual assault investigations where samples contain a mixture of DNA from a female victim and multiple male contributors. "It helps investigators identify and compare male DNA profiles, although it may not distinguish between men belonging to the same paternal lineage. The four males in this case were not related," the official said. Delhi Police submitted a 365-page chargesheet in the case on October 12, which details the investigation into the alleged sexual assault and murder. The chargesheet includes statements from 54 witnesses and mentions a gait analysis conducted on the accused, officers said earlier. The incident took place on September 11, and the girl's highly decomposed body was found in a field in Khadda Colony, Swaroop Nagar, on September 13....