I'm not sure specifically about his role in 'Police Story' without more research. But generally, he might have played a police officer or a character related to the police operations in the story.
Since Erik Estrada starred in 'Police Story', his performance was likely a significant part of what made the movie appealing. He may have used his physicality to great effect, perhaps in chase scenes or in confrontations. His facial expressions and line delivery would have helped to convey the character's thoughts and feelings. Moreover, his interaction with other actors in the movie would have created the relationships and tensions necessary for a good police - themed story. If he played a police officer, he might have shown the different aspects of the job, like the stress, the loyalty to the badge, and the relationships with the community.
In the 'the lyle and erik menendez story', Lyle and Erik Menendez are brothers. They are known for their heinous act of killing their parents. Their case got a lot of media attention and raised many questions about family and crime.
Erik is likely not based on a true story. Many such characters are invented to entertain or convey certain themes and messages, rather than being rooted in actual happenings.
In a different version, Christine gets lost in the opera house and Erik is the one who finds her. He could have been watching her from afar all this time. Instead of scaring her, he gently leads her to a safe place. They start talking about their dreams and fears. Christine realizes that Erik is not the monster everyone makes him out to be. This new understanding blossoms into love as they continue to meet secretly and share their innermost thoughts.
A simple fanfiction could be that Erik writes a beautiful song for Christine. When she hears it, she is deeply moved. She seeks him out to thank him. This encounter starts a series of meetings where they slowly fall in love. Their love is based on mutual respect for each other's talents.