Lai Junchen was said to be a thug who did not work, who was investigated for thievery while he was at He Prefecture (和州, roughly modern Chaohu, Anhui) and who then made false accusations against others to the prefect, Li Xu (李續) the Prince of Dongping, a cousin of then-reigning Emperor Ruizong.
Empress Dowager Wu believed him and thought he was faithful to her, and therefore made him a secret police official, rising to the rank of deputy imperial censor (御史中丞, Yushi Zhongcheng).
It was said that Lai Junchen personally retained a staff of several hundred men who were previously thugs, with the intent to have them make reports.
That year, a famous incident involving Lai and fellow secret police official Zhou Xing occurred.
(This incident inspired the Chinese proverb "invite the gentleman into the urn" (請君入甕, qing jun ru weng), now used for the concept of putting a person into a trap that he himself or she herself had set.)
Zhang, unable to stand the torture, yelled out to another official in charge of investigations, Xu Yougong (徐有功), who was known for being merciful.
In 692, Lai falsely accused the chancellors Ren Zhigu, Di Renjie, and Pei Xingben, along with other officials Cui Xuanli (崔宣禮), Lu Xian (盧獻), Wei Yuanzhong, and Li Sizhen (李嗣真) of treason.
Meanwhile, Lai falsely accused the minister of public works, Su Gan (蘇幹), of having been a co-conspirator of Li Chong's, and had him executed.
Lai was, however, thereafter again accused of corruption, and he was demoted to be a military officer at Tong Prefecture (同州, roughly modern Weinan, Shaanxi), interrupting his career as a secret police official.
Lai, wanting to monopolize the rewards for reporting this plot, was prepared to falsely accuse Ji of crimes as well, but Ji found this out and submitted a secret petition; he was able to meet Wu Zetian, who promoted him, while Lai was further restored to good graces in Wu Zetian's eyes and was promoted to be the deputy minister of husbandry (司僕少卿, Sipu Shaoqing).
It was further said that he created a book of the officials' names and then randomly chose whom to accuse by drawing lots, and that he compared himself to Shi Le, the founder of Later Zhao.
Meanwhile, Lai was said to be ready for something much more major—falsely accusing Li Dan, his older brother Li Zhe the Prince of Luling (also a former emperor), the Wu clan imperial princes, and Wu Zetian's powerful daughter Princess Taiping, of treason as well, to wipe them out gradually to give himself a chance to start a coup to seize the throne himself.
His friend Wei Suizhong (衛遂忠), publicly reported the plot, and the Wu clan princes and Princess Taiping responded by submitting accusations against Lai.
It was said that the people mourned Li Zhaode while celebrating Lai's death—with his enemies cutting out his flesh and organs, consuming much of it in anger.