A psychologist says an alleged Islamic extremist who has admitted killing two U.S. airmen at the Frankfurt airport earlier this year is mentally fit and can be held criminally responsible for his actions.

Psychologist Norbert Leygraf testified Monday to a Frankfurt state court that 21-year-old Arid Uka, an ethnic Albanian from Kosovo, suffered from no mental illnesses at the time of the March killing and remained in fine mental health, the dapd news agency reported.

Uka faces a possible life sentence if convicted of two counts of murder and three counts of attempted murder.

Uka has confessed to the killings, saying he was trying to stop U.S. servicemen from going to Afghanistan. Under German law the court still has to review all the evidence.