I'm skeptical of anything he says and consider everything a lie to fit his defense of himself. A couple things stand out. He claims she knew he was tracking her. That implies consent, which I don't believe for a moment. I also don't believe she even knew that he was tracking her, unless he told her just before he murdered her. He also claims she was upset that he was tracking her, PRIOR to her murder, and demanded he take the tracking device off her car. I think he's setting up a defense that her being "upset" is what drove him over the edge and which is why he killed her. I don't believe that either. I don't believe she would've been angry and belligerent as he's implying. She would've been, IMHO, terrified and gone to the police. I don't believe she would've confronted him, as he saying. I also don't believe they had a dinner date. I think that's ridiculous, especially as she already had plans to meet ACTUAL friends of hers for dinner. She wouldn't have had two dinner dates. He's implying they had a romantic relationship. As said upthread, I believe that was all in his head. Nothing of the kind was going on. Again, he's implying consent. That she allowed him to drive her vehicle and willingly went with him. I don't believe he gave her any choice. He had a gun. He could've threatened her, her husband, any number of things. She probably got into the vehicle because he was pointing the gun at her. Now he was in control, and he was going to make sure he was going to punish her for not acting according to the script he concocted. Just my opinion, he believed Masako was his because he wanted her. The fact that she didn't comply with his version of reality gave him the justification to hate her enough to end her life. I don't believe it was "if I can't have her, no one else can," it was more, "She's mine, she's not obeying me, so I have to kill her." That he is 75 makes no difference. He's not too old to be a sociopath. He doesn't deserve any sympathy due to his age. No doubt he played on her compassion due to his so-called "advanced" age and that he was "harmless" due to it. All you have to do is look at The Golden State Killer. He is unchanged and his age doesn't make him any less guilty. Same with this guy. His suicide attempt probably had more to do with "getting away with it" although there's also probably some attempt to avoid being humiliated. Not embarrassment, but humiliation.
I should say I firmly believe she did nothing wrong. I don't believe there was a "relationship" other than the one he tried to force on her. Being nice to someone or trying to help them is not a "relationship". Trying to avoid confrontation and being polite is not a "relationship". They were acquainted with each other. IMHO that's all there was. Anything else was something he fabricated, forced on her, believed himself and had no basis in reality.