The Islamic State claimed Masood as one of its own the next day in a statement to Amaq, a news agency affiliated with the group.
Basu said investigators have found no evidence to substantiate that claim but acknowledged that the group had influenced Masood.

“His methods appear to be based on low-sophistication, low-tech, low-cost techniques copied from other attacks and echo the rhetoric of [Islamic State] leaders in terms of methodology,” he said.

Police said Saturday that they believe Masood had acted without assistance from others and that his motives may never be fully known. Nine people arrested in the case have been released without charge, while two remain in custody.