Within minutes of a human dying, blow flies arrive on the scene. These carrion insects lay their eggs on the corpse, and forensics investigators can analyze the developmental stages of flies to determine when a person expired. But there are many different species of blow flies with species-specific developmental rates, and though telling their adult forms apart is clear, telling their eggs apart can be tricky. Researchers had two options to identify species: They could sample the larvae found on the corpse and grow them in the lab, which could take weeks, or choose DNA profiling, which is often expensive. Now, researchers have come up with a 3-minute method of categorizing the eggs laid by using an analytical technique called mass spectrometry, which gives a picture of the mass-based chemical composition of a sample, Chemical and Engineering News reports. The method is already being used in an active investigation by forensic scientists and is contributing to a growing database of blow fly egg profiles.