A woman who twice tried to gain access to a "highly restricted area" in Westminster before dumping two large knives nearby is being sought by Scotland Yard.
Detectives have released CCTV video footage of what they believe is the same woman pacing behind iron gates on two occasions.
After being refused entry, a scarf that the woman was believed to be carrying was later found on a wall wrapped around a pair of knives.
Scotland Yard tonight made an appeal to trace the woman on BBC One's Crimewatch, following the incident more than five months ago.
A statement said: "At around 3.30pm on Tuesday February 24, a woman asked a police officer for access to a highly restricted area, but was refused.
"Detectives believe this is the same woman recorded on a nearby CCTV camera at around the same time.
"Ten minutes after her first approach she returned to the secure area but again did not gain admission.
"Later a scarf, police believed to be carried by the woman, was found on a nearby wall wrapped around two large knives."
It is not being linked to any other incidents, police added.