Ben's Answering Machine

Why didn't the cops go to Ben's place and listen to his answering machine? As a fan of cops-n-robbers shows (CSI, Law&Order, etc) I took notice of the scene where Ben quietly lifted the phone and speed-dialed his own number and left the phone of the hook recording while sneaking up on Jake who was sitting on the rail of the balcony perfectly set up to get pushed off. I thought "Ben is very smart here." If he pushes Jake to his death then he just goes home and erases the message. If, however, something were to go wrong and he, Ben, ended up dead the evidence would be clearly recorded on the answering machine as Jake and Sandra were shouting things such as 'push the bastard!' 'kill the son of a bitch!' and other such phrases. I waited the rest of the movie for the cops to go to his house the play back the messages on his answering machine but it never happened. Why did the director use this device if the payoff were never coming? Anybody else notice this? It made the movie much less credible for me.