Something that has been bugging me... I thought in DC quicklime accelerated the decay and breakdown of bodies, thus making more recent murders seem much older. Could the murder actually be more recent than five years?
The clue that would make it clear what happened is whether there are any footprints in the quicklime. If the body is old, then whoever visited recently and rubbed the rust off should have left prints in the powder if they searched the place. It doesn't look like there are prints by the body, but I can't tell because there is no closeup of the area around the body.
Besides I am bothered by Rumi wanting to use quicklime for lines. She should be using chalk. Quicklime is caustic and irritating and not suitable for use around kids who have sensitive skin. The dust was used in ye olde days as ancient crowd control like blinding tear gas. Quicklime is also used for making concrete which is why I suspect there are bags of it lying around. Either way, Rumi's request to the DB was suspicious from the start.