The first time suspense is created in the stepfather is when David meets Michael, Susans son. The look Michael gives him when he shakes his hand seems awkward, like he already knows there something strange about him, Michaels eyes wander as if he feels uncomfortable. Although its the first time they meet, so he couldn't be curious about him already.
When the neighbour comes to the door and speaks to Susan about a crime watch programe she watched the night before, then Susan goes in to tell David the neighbour said there was a man who looked exactly like him on there but she laughs it off as if though it couldn't possibly be him. Michael meanwhile overhears this, which makes him question more who the man his mother is dating is. Suspense is created by David acting so cool and casual about it too, like its not him, glad he hasn't been sussed out yet.
Then by coincidence everybody apart from Michael thinks the lady across the street dies, who told Susan that David was a murderer. She was pushed down the stairs rather than fell, which makes you think that man killed an innocent lady to keep it quiet about a suspicion only she had, to begin with. Then Michael's suspicion grows as he assumes it was David who did it.
Finally it is odd how David will never give bank details or other information to the people he works for, where Susan got him a job. At first the friend assumes he is busy and is putting it off because he has other things to do, however, this continues which leads to her being more suspicious also. The friend asks Susan why he's acting like this, but she shuns it off as if though its unintentional. Suspense is created throughout the film, having you question David's character and what he's done.