Detectives investigating the murder of sub-postmaster's son Craig Hodson-Walker have made a ninth arrest.
West Mercia Constabulary said the woman was detained at an address in Birmingham on suspicion of assisting an offender.
The development follows the arrest of four people on suspicion of murder and attempted murder and another four people on suspicion of assisting an offender yesterday morning.
Mr Hodson-Walker, who was 29, died after being shot in the chest during an armed robbery at the sub-post office in Fairfield, Worcestershire, last Friday.
A police spokesman said: "Those arrested remain in custody assisting with inquiries at police stations across the West Mercia and West Midlands force areas."
Officers have confirmed that five of the suspects being questioned are men and four are women.
Meanwhile, police are continuing to appeal for anyone with information regarding the murder investigation to contact the West Mercia force on 0300 333 3000 or the Crimestoppers hotline on 0800 555 111.