<sod >A French police officer and his wifeÂ have been killed in knife attacks by an unknown assailant, who has now been shot dead by police after a tense stand off.< eod>< sod > A French police officer and his wife, who worked for the Ministry of the Interior,Â have been killed in knife attacks by an unknown assailant, who has now been shot dead by police after a tense stand off in the family home.< eod>