It may be difficult to prove whether the British diver charged with the involuntary homicide of his girlfriend and another diver last year was responsible for their deaths, according to a top criminal lawyer.

Experienced diver Stephen Martin is charged with the involuntary homicide of two divers, due to alleged negligence.

“It’s not a black or white matter. It really does depend on the evidence and specifics of the case. The prosecution will have to prove that he was responsible for them during the dive,” lawyer Stefano Filletti told the Times of Malta.

He was speaking on the case of UK diver Stephen Martin, who is fighting an extradition order to face charges in Malta that his negligence resulted in the deaths of two divers, one of whom was his longstanding partner.

Larissa Hooley, 48, and Nigel Haines, 59, died during a diving trip in Gozo last summer.

Ms Hooley had developed an immersion pulmonary edema – a condition similar to altitude sickness and common among mountain climbers – during the dive and is believed to have died while still submerged.

Mr Hianes died during the frantic rescue attempt that ensued.

The Maltese authorities are alleging that Mr Martin, a qualified diving instructor, was negligent when he did not immediately notice Ms Hooley was in distress. They argue he should not have authorised the dive in the first place due to poor weather conditions and that the descent and ascent during the rescue were “irregular”.

It’s not a black or white matter

If Mr Martin is found guilty, he could face up to 10 years in prison.

He insists, however, that he was not acting within his capacity as a diving instructor and had not authorised the dive himself.

“I wasn’t responsible for the group. We were all qualified and were diving together. We were responsible for ourselves,” he said from his home in Rustington, West Sussex.

Dr Filletti said the legal situation was complex and the onus to prove Mr Martin was responsible for the group fell on the prosecution.

This is where the situation gets tricky. Mr Martin’s legal team told the Times of Malta they were being “kept in the dark” by the Maltese authorities, who were refusing to disclose the evidence they had.

Lawyer Larry Formosa, who is representing Mr Martin in Malta, said the defence was considering filing a case before the Constitutional Court over the non-disclosure of evidence.

Experts within the local diving community have raised concerns that Mr Martin’s case could set a dangerous precedent.

“These deaths occurred as part of a failed rescue attempt. Does this mean that unless your rescue is successful you are responsible for any deaths?” one senior diving instructor, who asked not to be named, said.

Asked about this, Dr Filletti said this depended on the type of negligence.

The head of the Criminal Law Department at the University of Malta, Dr Filletti said that negligence was divided into two categories: the lack of observance of rules and regulations, including industry standards, and the failure to provide a reasonable standard of care.