The police have made no progress in the investigation into the death of Charles Brignone, who suffered fatal head injuries after being struck by a boat propeller while snorkelling off Marsascala earlier this month.

Investigators are finding it increasingly difficult to trace the boat that killed the snorkeler and are hoping more witnesses come forward.

Sources close to the probe said police had received “pointers” but although boat owners were questioned, they had no firm evidence any were involved.

The sources said evidence, such as blood, would have been washed away within minutes.

It was also “nearly impossible” to establish the size of the boat based on the head injuries.

Mr Brignone, 44, was on a family camping trip in Żonqor, near Marsascala, when he went snorkelling at 10 a.m. on August 4.

When he failed to return by mid-afternoon his wife Josianne called for help. His body was found the following morning.

An autopsy indicated he died of skull lacerations, which sources said could have been caused by a boat propeller.

As a result, the police are treating the case as involuntary manslaughter.

Investigators have analysed the Armed Forces of Malta’s maritime radar footage but the spots that can be seen on the screen could have been boats, large waves or even birds.

It also emerged during the investigation the cord attached to Mr Brignone’s buoy marker was not torn or damaged in any way, indicating it was not hit by the propeller that caused his death.

The cord was only six metres long, which means that Mr Brignone might have removed it to be able to dive deeper.

As the investigations continue, boat owners are being urged, through Transport Malta’s Safety at Sea Campaign, to respect regulations that stipulate that boats should steer 100 metres clear of snorkelers’ buoys.

By law, a boat cannot travel over 10 knots if within 200 metres of the shore and 300 metres from a sandy beach.