The firebombing of an immigration centre in Dover was motivated by a terrorist ideology, Counter Terrorism Policing South East has said, citing recovered evidence.
Andrew Leak, 66, from High Wycombe in Buckinghamshire, is believed to have killed himself after throwing two or three "crude" incendiary devices at the Western Jet Foil site, in Kent, last Sunday.
The counter terror police said a number of "significant witnesses" have been spoken to and a number of items of interest have been recovered.
Evidence from examining digital media devices found during the investigation is said to suggest "an extreme right-wing motivation behind the attack," officers said.
They added: "There is currently nothing to suggest the offender was working alongside anyone else and there is not believed to be any wider threat to the public."
Kent Police said "two to three incendiary devices" were thrown at the centre by "a single suspect who arrived at the scene in a car".
Two people suffered minor injuries and the suspect was later found dead at a nearby petrol station, the force added.
Tim Jacques, senior national co-ordinator for Counter Terrorism Policing, said: "Assessing when this crosses the terrorism threshold is a complex process and needs to be carefully considered on a case-by-case basis.
"These decisions need to be determined by the facts, as far as they can be established at any given time.
"After considering the evidence collected so far in this case, whilst there are strong indications that mental health was likely a factor, I am satisfied that the suspect's actions were primarily driven by an extremist ideology.
"This meets the threshold for a terrorist incident."
Facebook posts on a now-deleted account under the name of an Andy Leak from High Wycombe contain anti-Muslim sentiments and complaints about people claiming benefits if they do not speak English.