A retired detective has told Ian Bailey's damages action that it is not a legitimate garda technique to arrest a partner in order to put pressure on a suspect.
The former journalist is suing the State and Garda Commissioner for alleged wrongful arrest over the Sophie Toscan du Plantier murder in west Cork in December 1996.
His partner Jules Thomas was also arrested for questioning in February 1997 as part of the investigation.
State witness retired detective James B Hanley, who was involved in the case, is being cross examined.