If he/she has a terrorist motive, it's more than likely that they would have been radicalised online. Nearly all Islamist/Far-right attacks over the past few years have involved radicalisation through the internet, although many have been assisted through real people.

For example, one of the Bethnal Green Trio was Shamima Begum (recently in the news for attempting to come back the UK), and her father attended many Anjem Choudary speeches - a hate cleric who is currently in jail.