Vaginal swabs are considered as most probative evidence material in sexual assault cases to get the DNA profile of the perpetrator. With the increase in post-coital interval, the possibility to get the autosomal DNA STR profile of the perpetrator diminishes rapidly from an alive victim. This becomes more serious problem especially when victims of rape cases provide vaginal swabs after several days of the incidence. The study was designed to find the time interval at which autosomal STR system fails to generate the DNA profile the semen donor in the post-coital vaginal swabs. Sixty two post coital vaginal swabs (x3) were collected from six volunteers at different TSI (time since intercourse). Out of these, 42 post coital vaginal swabs (up to TSI 5 days) were used to generate the autosomal DNA profile of the semen donor and twenty of the post coital vaginal swabs obtained at the TSI of 6, 7, 8, 9 and 10 days were not tested for autosomal STR profile and were saved for subsequent analysis of Y-STRs. It was found that autosomal DNA profile of semen donor up to TSI 48 hours is feasible; however, chances of getting complete male DNA, partial male DNA profile and no male profile at TSI 72 hours are 17%, 67% and 16% respectively. Chances of getting complete male DNA profile becomes zero at TSI 96 hours, however, partial male DNA profile is accessible (40%) at TSI 96 hours. It is concluded that autosomal DNA STR system becomes fail to generate the DNA profile the semen donor in the post-coital vaginal swabs at TSI >96 hours.