Liverpool Suicide Bomber Had Been Planning Attack Since April

British police investigating the Liverpool taxi explosion said on Wednesday that the suicide bomber had been planning the attack since April and had been making “relevant purchases” for the bomb at least since then.

Emad Al Swealmeen, 32, died when the blast from his homemade bomb exploded from inside the passenger seat of a taxi outside Liverpool Women’s Hospital on Sunday morning. The taxi driver reportedly noticed the suicide bomber, locking him inside his vehicle and reducing the damage inflicted by the attack. The taxi driver, who escaped seconds before the explosion, was left with a few minor burns and had shrapnel in his body but was discharged on Monday.

Russ Jackson, the head of counterterrorism policing for northwest England, said investigators so far had not found any other people “of concern” and added that they are still trying to find the motive for the attack, which was being treated as a "terrorist incident."

“A complex picture is emerging over the purchases of the component parts of the device. We know that Al-Swealmeen rented the property from April this year and we believe relevant purchases have been made at least since that time,” Jackson said.

Al Swealmeen has had “episodes of mental illness” in the past and investigators are still trying to fully understand what part this played in the attack, the Guardian reported.

The attacker was reportedly born in Iraq and applied for asylum in Britain in 2014, but was denied. It is unclear what his legal status was at the time of the bombing, the Associated Press reported.

Home Secretary Priti Patel said the U.K. terror threat level had been raised to "severe," meaning an attack is "highly likely" given that the explosion in Liverpool was the second terror incident in a month.