LONDON -- Police say three British schoolgirls who travelled to Syria to join the Islamic State group won't be prosecuted for terrorism if they return.

Mark Rowley, head of counterterrorism for the Metropolitan Police, said Tuesday that "we have no evidence to support their involvement in terrorism."

The journey of the three 15- and 16-year-olds last month has left their families bewildered and angry.

Relatives say police failed to inform them that a friend of the trio had travelled to Syria in December. They say had they known they would have looked for warning signals.

Sahima Begum, whose sister Shamima is one of the girls, said she was an ordinary teen who showed no signs of radicalization and "used to watch 'Keeping up with the Kardashians' and things like that."