Story highlights 17 police officers are under investigation for possible mishandling of Stephen Port'scbs case

Rape victims only went to police after killings became known

London (CNN) London police are reviewing the deaths of dozens of men who used sex-enhancing drugs amid concerns that cases previously dismissed as drug overdoses may be additional victims of serial killer Stephen Port.

Port, 41, was found guilty of murdering four gay men and drugging and sexually assaulting seven others by a jury at London's Old Bailey on Wednesday.

The Metropolitan Police Service told CNN they had identified at least 58 deaths from poisoning by the date-rape drug GHB between June 2011 and October 2015 -- the period in which Port carried out his crimes.

Victim Anthony Walgate

"It is not known if these deaths were related to chemsex activities. In many cases police involvement was limited, with the matter dealt with by the coroner," a police spokesman told CNN. "A review of these deaths is now underway to establish any suspicious circumstances."

Police say there is so far nothing to suggest the cases are linked to Port.

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