A 20-year-old man accused of killing the police officer Andrew Harper has had the murder charge against him dropped after spending a month in custody.

Prosecutors said they were no longer pursing the case against Jed Foster, from Burghfield in Berkshire, who was arrested within an hour of Harper’s death on 15 August and charged four days later.

On Wednesday, three teenagers were charged with Harper’s murder. Henry Long, 18, from Mortimer in Reading, and two 17-year-old boys, who cannot be named because of their age, appeared at Reading magistrates court on Thursday.

They, along with Thomas King, 21, from Basingstoke, are also accused of conspiracy to steal a quad bike.

The area’s chief crown prosecutor, Jaswant Narwal, said: “The CPS has discontinued the case against Jed Foster, 20, in relation to the ongoing investigation into PC Harper’s death in Berkshire.”

Speaking outside court following his first appearance, Foster’s lawyer, Rob Jacques, said: “On behalf of him and his family he emphatically denies any responsibility or involvement in the horrific murder of PC Andrew Harper.”

Foster’s mother, Jolene Hannington, protested her son’s innocence shortly after he was charged. She wrote on social media: “We will fight this and hopefully someone that knows the truth will come forward and tell the truth or live the rest of their lives knowing they let an innocent boy go away for something he didn’t do.”

Harper, 28, who had recently got married, was killed near the village of Sulhamstead in Berkshire when he was dragged under a van while responding to reports of a burglary.