Scotland Yard Flying Squad Chief Commander Frank Cater was appointed to lead the hunt for the thieves. Given the boldness and highly skilled nature of the operation, the police were quickly able to narrow down the list of potential suspects to McAvoy and Robinson, who had not been particularly secretive about recruiting participants for a rumoured 'inside job' that they had planned. Robinson, whose nickname was 'The Colonel', was already well known to the police, while McAvoy was considered to be one of South London's most prolific armed robbers.
Quickly realising that the sheer knowledge available to the gang pointed to an insider participant, the police soon came across Anthony Black, who had been late to work on the day of the robbery and who had missed the entire heist. The connection to Robinson’s sister led to a swift confession by Black, who gave up the names of the newly wealthy McAvoy and Robinson.
Neither McAvoy nor Robinson helped themselves by 'laying low'. Within weeks of the heist, both moved from humble South London council houses to a grand estate in Kent, paid for in cash. Rumours that McAvoy had bought two Rottweiler dogs to protect his mansion and named them 'Brinks' and 'Mat', did not win him any awards for subtlety.