"We still believe that Masood acted alone on the day and there is no information or intelligence to suggest there are further attacks planned," Senior National Coordinator for UK Counter Terrorism Policing Neil Basu said, as cited in a in a statement released by the police late on Saturday.
Basu added that the police still need "to establish with absolute clarity why he did these unspeakable acts," stressing that the reasons behind the attack "may have died with him [the attacker]."
"Nevertheless, we are determined to understand if Masood was a lone actor inspired by terrorist propaganda or if others have encouraged, supported or directed him. If the latter proves to be the case, they will face justice," Basu stated.
On Wednesday, Masood, 52, drove his car into pedestrians on Westminster Bridge in the center of London. He then left the car, armed with a knife, and attempted to enter the parliament building. The attack left five people dead, including the attacker, and at least 50 people injured. Daesh terrorist group has claimed responsibility for the attack.
The attacker was born in Kent and lived in West Midlands, according to Metropolitan Police. He had several previous convictions for assaults and possession of offensive weapons. The last conviction was in 2003.
