Kent Police said it was being assisted by Thames Valley Police in its probe of the attack at The Viaduct on Sunday and that it had searched a property in the High Wycombe area.
The man suspected of carrying out the attack was found dead at a nearby petrol station, and two people suffered minor injuries in the attack.
High Wycombe is about 118 miles from Dover.
A photographer with the news agency Reuters, who witnessed the incident, reported seeing a man had thrown petrol bombs with fireworks attached before taking his own life.
The attacker was described as a white man wearing a striped top, who drove up to the centre in a white Seat four-wheel drive vehicle, the agency reported.
In a statement, Kent Police said they had established that two to three incendiary devices were thrown by the suspect.
It said that its Explosive Ordnance Disposal Unit found a further device in the suspect’s car, which was confirmed safe.
Speaking after the attack, the MP for Dover said she was “deeply shocked”.
Natalie Elphicke said: "I am deeply shocked by the firebombing at the Dover migrant processing centre this weekend.
“Tensions have been rising following an incident the previous weekend and the large numbers of illegal arrivals in recent weeks. The situation on the ground is concerning.
“It's now vital to get a grip on the small boats crisis. The Prime Minister Rishi Sunak and President Macron should urgently seek to reach a new agreement for joint patrols and a joint Channel security zone in order to bring an end to these dangerous and illegal crossings.”
The site remained open, however around 700 people at the site were relocated to Manston migrant holding centre for safety reasons during the initial response.
Suella Braverman is expected to be questioned about the problems at the site in Kent when she appears in the House of Commons later Monday.
Backbench MP Sir Roger Gale said overcrowing at the facility in his North Thanet constituency was “wholly unacceptable” and that there were more than 4,000 people at the facility. He said it was a “breach of humane conditions”.