I haven't ruled it out that some of the deaths might have been suspicious, in fact I think a few of them probably where. But I think these where individual incidents, not the work of a serial killer. It's pretty normal for a big city to have its fair share of murders.
Maybe the lad screaming on the phone was the victim of an attack, who knows. Maybe he got into a dispute with someone and they attacked him. But to say that is linked to the deaths of another 27 people, where there was no evidence of an attack is somewhat far fetched.