Characters in A Thriller Opening

Watching a number of Thriller openings in lessons has made me notice that there isn't that more characters in the opening of a thriller.
The audience isn't really introduced to all the characters as that would just give away the film, with not alot to discover.
In THE STEPFATHER (2009) I saw that there was only one living character in the scene in the begging. Later in the opening shots of a dead family was shown as well as flash backs of a girl screaming.

In PYSCHO(1960) there is only one character in the opening and then the shadow of a killer.

I think that it is better to limit the number of characters in a  thriller opening as it mantains the high level of suspense and the audience can focus on that one character- either acknowledging that it is the main character or something drastic will happen to them.
In our thriller opening there will only be one character shown as she is the main character and also, the hand of a victim will be shown .. but not the face.