Human sacrifice was a common institution in Mayan culture, albeit not always with the extremity of the Aztec Empire. The purpose of these ritual killings was to appease their pantheon of gods, who would ideally provide prosperity in exchange for their satiated blood-lust. Sacrifices would be brought to the alter of their respective community and have their lives ceremoniously ended with an obsidian blade. But to satisfy the rain god Chaak, the protocol was a bit different in detail.
Sacrifices to Chaak were painted blue, which the Mayans believed was a symbol of water’s healing properties (via Reuters). Then, either with or without the otherwise standard heart removal, they were cast into the massive sinkhole known as the Ik Kil cenote alongside pieces of similarly painted pottery (via Live Science). As “only” 120 individuals have been distinguished from the remains found, it is unlikely this practice was routine — it was probably used more as a last resort.