(Isabel Le Blanc-Louvry and colleagues, Forensic Science International)

Two research papers published this week throw further light on the health risks of the Taser stun gun. This striking image shows the central issue examined in one of the papers: what happened when a barbed dart fired by a police Taser struck a 27-year-old man on the side of the head.

Although Isabel Le Blanc-Louvry and colleagues at the department of forensic medicine at Rouen University Hospital in France do not reveal when or where this occured, they say the victim had been drunk and resisted police requests for his ID.

The police fired the pneumatically powered Taser to incapacitate and subdue him - but somehow nobody noticed a dart remained stuck in his head, until he later went to hospital complaining of a persistent headache.

In the ER, the dart was found to "have penetrated the frontal part of the skull and damaged the underlying frontal lobe", the team report in Forensic Science International. "We observed that the length of the Taser dart is sufficient to allow brain penetration," they write. The man made a full recovery.

The controversial weapon's woes continued in the journal Circulation this week, where cardiologist Douglas Zipes at Indiana University School of Medicine in Indianapolis reports that Taser strikes near the heart can kill.

In a study of eight cases where cardiac arrest was induced after tasings by US police departments, seven victims died. "Electronic control device stimulation can cause cardiac arrest" due to ventricular tachycardia and fibrillation, he concludes.

Although more recent advice from Taser International, the Scottsdale, Arizona-based maker of the weapon, is for officers to avoid the chest area when firing its stun guns, in the melee of a police operation that is not always possible.

Last year, a teenager died after being tased in the chest and his parents were awarded $10 million in damages - an amount Taser has since had reduced to $4.3 million on appeal.

In February, Amnesty International calculated that 500 people in the US have died following tasings.

Hat tip: David Dobbs at Wired.