The guilty verdict in the Stephen Port murder trial is welcome but no recompense for the lost lives of four young gay men; some of whom may have died needlessly because of apparent police failings.

Port’s killing spree began with three murders between June and September 2014. The victims were lured to his flat and given fatal doses of the drug GHB. All three bodies were dumped in or near St Margaret’s churchyard in Barking, east London.

To have three men in their 20s found dead in public places in mysterious, unexplained circumstances, and close to each other in time and place, should have triggered alarm bells. But even after the third murder, police still maintained the deaths were “unusual” but “not suspicious”.

Right from the outset, officers rebuffed all suggestions of foul play. Kiera and China, friends of the first murder victim, Anthony Walgate, raised queries but say they were given the brush-off by the police, who they described as “unhelpful and unsympathetic”.

In October 2014, I was contacted by John, an ex-flatmate of Gabriel Kovari, the second man to be murdered. John told me he went to the police to express his concern about Gabriel’s death and that of the other two men. Anxious for his own safety, he mentioned the possibility that it was murder and that the three deaths might be linked. The police advised him there was nothing to worry about; suggesting that the deaths were not murder and not related.

After initial contact with the police, he heard nothing more. He said he tried to get updated information from officers but claims it was very difficult. The police struck him as not interested and not willing.

I advised John to contact Pink News and the LGBT police monitoring group, Galop, with a request that they press the police for answers. He says they did so, but were told by officers that the deaths were not murder and that there was no serial killer.

John also raised his concerns at the inquest into Gabriel’s death. But these concerns were dismissed. He told me that he did not have confidence in the police handling of the killings. He felt the police were not taking the odd, unexplained deaths seriously. It seems he was right.

Serial killer Stephen Port. Photograph: Rex/Shutterstock

Shockingly, even after the second and third murders, the police did not issue a public alert to the LGBT community that a serial killer could be on the loose. This failing ignored Metropolitan police best practice advice which was agreed two decades ago, after previous murders of gay men.

The first police public appeal for information was not made until October 2015, after the fourth murder and after Port had been charged. It was a year too late. Four young men were already dead. This appeal should have been made in August 2014 after the first two killings. If the police had done this, further deaths may have been prevented. Two of the men might still be alive.

There was a host of errors in the police investigation. Officers let Port slip though their fingers. He had been arrested after the body of Anthony Walgate was found in June 2014 and was later jailed for perverting the course of justice over untruths about his contact with Walgate. Port’s lies should have raised red flags but instead officers accepted his explanation concerning drug use by Walgate.

Equally incredible, police failed to adequately check the handwriting on the fake Daniel Whitworth suicide note, which had been penned by Port to cover up his responsibility for Whitworth’s murder. As far as we know, there was no thorough fingerprint and DNA testing of the note, which may have led direct to Port given that he had been previously arrested in connection with Walgate’s death and was presumably fingerprinted and DNA-sampled.

If four young middle-class men had been murdered in Chelsea, police would have probably made a public appeal much sooner and mounted a far more comprehensive investigation. In contrast, the murder of low-income gay men in working-class Barking was treated very differently. Whether conscious or unconscious, police officers stand accused of class and sexuality bias.

The police mishandling of the Port murders echo their previous failings in other serial killings of gay men, including those by Dennis Nilson, Michael Lupo and Colin Ireland. The lessons from those much-criticised investigations have still not been learned.

Although police relations with the LGBT community are vastly better than two decades ago, this case is a wake-up call regarding the continued inadequate attitudes and behaviour of some officers.

It seems likely that biased assumptions about gay men and drug use played a role in the police shortcomings with regard to these murders. This could amount to institutional homophobia, similar to the institutional racism identified in the Macpherson report. Such a possibility should be investigated and ruled on by the Independent Police Complaints Commission (IPPC).

• Peter Tatchell is Director of the Peter Tatchell Foundation: www.PeterTatchellFoundation.org @PeterTatchell