From reports generated by the official police investigation, the man who appeared at Lu Dayong's apartment door was about 1.8 meters in height. This man got into a dispute with Lu Dayong at the entrance. The man was initially suspected to likely be a debt collector from an online loan company.
However, the police had conducted a thorough investigation of all the creditors who had made online loans to Lu Dayong and it was determined no debt collectors from them were sent to Lu Dayong's home on that day.
So they had ruled out the man being sent by an online loan company.
Yet this did not rule out debt collectors from private loan companies.
That kind of lending business was illegal, so they certainly wouldn't come up to the police and confess they had sent someone there.
The case had eventually come to the point that it was already considered by most to be a "cold case," by then. It would likely have lost any chance of a follow up within a few years.