Jessica and Jacques Moretti are under criminal investigation for involuntary manslaughter, as well as bodily harm and arson through negligence.

Police say the suspect's firearms licence expired two years ago, and exactly who owned the guns used in the attack is unclear.

Somali Islamist militant group al-Shabab has staged several attacks in Kenya, prompting the border to be closed.

The charge was brought after the Council of Europe lifted his immunity, which he had as its former secretary general.