Police are looking for a naked cyclist stalking female joggers in west London.
Detectives are examining a series of sightings of him close to the River Thames in Barnes.
Women have seen the man, either completely naked or naked from the waist down, exposing himself on towpaths and riverside roads.
But despite a large number of reports and in one case a woman recognised the man again when fully clothed, officers have not been able to identify him.
Senior officers are concerned about the incidents, especially after the man attempted to speak to several women.
Three women made official complaints over the summer but officers are also following up a series of sightings in recent weeks.
The first reported incident took place in May when two girls, aged 15 and 16, saw the semi-naked man get on a bicycle in Londsale Road.
In June, a second crime report was made when a 28-year-old female jogger saw the man hiding in undergrowth on the towpath between Kew Green and Twickenham Bridge.
As she returned, the man, who was semi-naked, attempted to speak to her before cycling away.
In July, a woman jogger in her early 20s reported that a naked man cycled past her on the towpath between Barnes Bridge and Hammersmith Bridge.
A Metropolitan Police spokesman said: "We are taking this extremely seriously and need to identify this man as a matter of urgency.
"The isolated locations that these incidents have occurred coupled with the lone female victims increases our level of concern."
The cyclist has been described as white and about 30 years old.