Khalid Masood’s motivations and associates are still being investigated.
The detained suspects in connection with the Westminster attack have been released with “no further action”.
On Saturday, the Metropolitan Police freed a 30-year-old from Birmingham who was originally held on suspicion of preparing terrorist acts, he was the final man in custody.
Previously, the eleven others who were arrested in connection with the investigation have been released. However, “inquiries continue” according to Scotland Yard
Potential accomplices, were being searched by investigators, who may have helped Khalid Masood plan or carry out his attack.
The fact that he used WhatsApp just minutes before ploughing his car into pedestrians on Westminster Bridge increased suspicions over a potential wider extremist network.
Injuries sustained during the rampage killed British mother Aysha Frade, pensioner Leslie Rhodes and American tourist Kurt Cochran.
Afterwards, Masood crashed into railings outside the Houses of Parliament and ran into an entrance where he stabbed PC Keith Palmer to death, before being shot dead by armed police.
According to investigators, Masood may have been inspired by Islamist terrorism. ISIS has claimed responsibility for the attack, although the extent of their involvement is not yet known.
Mark Rowley, Scotland Yard’s acting deputy commissioner said they were investigating if the attacker acted completely alone after being inspired by terrorist propaganda or was “encouraged, supported or directed” by others.
Neil Basu, deputy assistant commissioner, stated that investigators had not yet found any evidence of a direct link despite that the method of attack, following Isis propaganda instructions on using cars and knives, “echoed Isis rhetoric.”
He added “Whilst I have found no evidence of an association with Isis or al-Qaeda, there is clearly an interest in jihad.”
The Home Secretary is set to meet with technology companies this week to address removal of extremist material online after questions over whether Masood may have been radicalized in part online.
Masood’s motive has not yet been established by investigators. The 52-year-old man is a Muslim convert who had a lengthy criminal history and lived in areas including Sussex, Birmingham and London.
Exactly a week after the attack on Wednesday, thousands of people joined hands in a vigil for the victims, while further tributes have been paid across the country.