British police are appealing to the public to help identify aspiring terrorists after the murder of an American journalist focused attention on extremism in the U.K.

Assistant Commissioner Mark Rowley said Tuesday that the involvement of a person of British nationality in James Foley's murder underscored the need to identify those who might travel abroad to fight or are at risk of being radicalized.

Rowley says investigators are making significant progress in the inquiry into Foley's murder "but we will not be giving a running commentary."

Authorities underlined their commitment to fighting the threat of people going to the Middle East to take part in jihad amid fears former fighters will return home to launch attacks. Rowley said 69 arrests have been made in the first half of the year.