Action Comics #654 (1990)

After thwarting Intergang's attack on Lex Luthor's country estate, Batman and Superman hear the sound of a demolished building. Superman finds Gangbuster's helmet among the debris, but the vigilante somehow survived the demolition and briefs Superman on the attack he suffered at the hands of Shockwave and Chiller. Suddenly, Shockwave rises from the debris and attacks Superman and Gangbuster. Superman defeats him, and Shockwave tells them where Intergang is holding Cat Grant hostage. In an outlying industrial park, Doctor Moon prepares Cat Grant for a brain-washing process to change her testimony against Morgan Edge in the upcoming trial. But the process is stopped before it even begins, as Batman, Superman, and Gangbuster break into the facility. The trio defeats Intergang's men and saves Cat Grant, but Batman disappears from the scene, leaving a note for Superman saying he'll know where to find him. Superman finds Batman in Amanda McCoy's messy apartment. Batman shows Superman the diary of the doctor, where she wrote all about her investigations regarding Superman's real identity and how Lex Luthor discredited her discovery. She would later try to prove Superman's duality with the help of a private detective named Matt Stockton, who eventually died at the hands of Intergang during the investigation. The final entry in her diary reads about her stealing Luthor's Kryptonite Ring to confront Clark Kent and force him to admit he was Superman. Batman concludes that after her confrontation with Kent at the cemetery, she was killed by some muggers who stole her purse and looted her apartment. Batman also reveals he had the ring during the last few days and handles it to Superman. He leaves and suggests he take all the evidence about his identity before the police find it. The next morning, Bruce Wayne reads about Morgan Edge's guilty verdict and the report of Amanda McCoy's death in the newspaper. Suddenly the Bat Cave alarm is activated. Bruce changes to his Batman suit and finds out Superman is the intruder. Superman tells Batman about how some villains attempted to subvert his will and his fear that someday they might succeed. He trusts Batman enough to give him the responsibility to conserve the Kryptonite Ring, giving him the means to kill him if that day comes.