People still managed to piece together evidence base on experiments and experience. For example there's a Chinese book written in 1247 titled Collected Cases of Injustice Rectified. It described in great detail on the science of forensics. The first volume described methods on post-mortem examinations. The third, fourth, and fifth volumes detail the appearances of corpses from various causes of death and methods of treatments to certain injuries. Here's one case it documented:

A local peasant from a Chinese village was found murdered, hacked to death by a hand sickle. The use of a sickle, a tool used by peasants to cut the rice at harvest time, suggested that another local peasant worker had committed the murder. The local magistrate began the investigation by calling all the local peasants who could be suspects into the village square. Each was to carry their hand sickles to the town square with them. Once assembled, the magistrate ordered the ten-or-so suspects to place their hand sickles on the ground in front of them and then step back a few yards. The afternoon sun was warm and as the villagers, suspects, and magistrates waited, bright shiny metallic green flies began to buzz around them in the village square. The shiny metallic colored flies then began to focus in on one of the hand sickles lying on the ground. Within just a few minutes many had landed on the hand sickle and were crawling over it with interest. None of the other hand sickles had attracted any of these pretty flies. The owner of the tool became very nervous, and it was only a few more moments before all those in the village knew who the murderer was. With head hung in shame and pleading for mercy, the magistrate led the murderer away. The witnesses of the murder were the brightly metallic colored flies known as the blow flies which had been attracted to the remaining bits of soft tissue, blood, bone and hair which had stuck to the hand sickle after the murder was committed. The knowledge of the village magistrate as to a specific insect group's behavior regarding their attraction to dead human tissue was the key to solving this violent act and justice was served in ancient China.

Here's an old translation of the book (large PDF file).