Who would have thought double homicide could be so, well, dull? In fairness, the murders are carried out off-stage, before the action of this play starts, but playwright Emily Mann has still crafted a rather listless piece from one of the most dramatic moments in the gay rights movement. Part of her problem is that most people watching the play, myself included, already know the bones of what will happen: Harvey Milk, the first openly gay person to be elected to office in the US, was shot and killed by Dan White, along with the Mayor at the time. White was found guilty of “voluntary manslaughter” instead of first-degree murder, which lead to riots which were dealt with violently by the police. So far, so dramatic.

Unfortunately, the reality of the situation is so dramatic and tragic, and Milk himself had such an eloquent turn of phrase, that Mann’s attempt to dramatise it fall rather flat. The extended court-room scene is leaden and drags, making the play feel longer than its hour and 40 minutes. Further, the court-room testimony, which draws heavily on verbatim text, is intercut with witness reports, character reports and  remembrances from those who knew the murdered men, making the whole piece feel disjointed. This is compounded by the staging (James Turner): the minimal court setting sits in between two banks of seating. This has the effect of half-heartedly putting the audience in the position of the jurors, but also means that the action – such as it is – takes place on a long, thin strip of stage, making me feel as though I was watching a slightly tedious tennis match.

Director Joss Bennathan also intercuts the piece with video footage, both of Milk himself and of the riots. The most powerful image in the whole piece is footage of the candle-lit march and vigil that was held, peacefully, immediately after Milk and Moscone were shot and killed. Unfortunately for Mann and Bennathan, this image is so striking that the remaining 20 or so minutes of the play feel superfluous.

Christopher Lane as the lawyer for the defence is superb, weaselling his way to a verdict of voluntary manslaughter instead of pre-mediated murder, but the script does not allow us to understand much of his motivation, nor does it allow him much depth. He does a remarkable job of making himself both hateful and understandable, but is not a well-rounded character. Philip Duguid-McQuillan also does a fine job of playing Dan White – a manic-depressive who had a momentary breakdown, or a bitter homophobe carrying out a politically motivated assassination? It’s not left ambiguous that a miscarriage of justice has been perpetrated here, removing a great deal of potential suspense. This, coupled with too much dependence on loud noises and bright lights (George Dennis and Richard Williamson, respectively) to bring tension, makes what should be a powerful play feel rather flat.

In the end, it is the weight of its authenticity which drags it down – it makes one realise how cumbersome are the machinations of justice systems, and made me never want to be called for jury service.

Execution of Justice is at Southwark Playhouse until 4 February. For more information, visit the website here: http://southwarkplayhouse.co.uk/whats-on/