Senior officers from the investigation asked for assistance from the National Policing Improvement Agency , which provides expertise for difficult cases. On 4 January 2011, a clinical forensic psychologist , who had previously been involved as a criminal profiler in other high-profile murder cases, joined the investigation to help narrow down the number of potential suspects.  Jones stated that his officers had established over 1,000 lines of inquiry.   Jones said, "I can assure you, we are determined to solve this crime and bring Jo's killers to justice."  On 5 January, Detective Chief Inspector Jones announced that one of Yeates' socks was missing when she was found dead and that it had not been found at the crime scene or in her home.