Cab Coordinator reported he did not inform Local Control of an overtake on final; citing being distracted by other duties and not receiving adequate training. Reporter stated no one else noticed it either.

Narrative

Aircraft X and aircraft Y were on approach for Runway 31R when aircraft Y had a 40 KTS overtake on aircraft X. At the time I was working Cab Coordinator position. The Local Controller had just landed 2 Falcons back to back on Runway 13L and had releases on two jets off that runway. I had multiple prop aircraft and jet aircraft that needed releases on both runways. I was focused on what space Local would have to depart the aircraft and who I should be calling on to get their releases so I could help keep delays to a minimum. While I was reviewing my strips as Cab Coordinator I did not notice that the separation between aircraft X and aircraft Y was decreasing and fell below 3 miles. I would also like to mention there was a Supervisor on duty and a 'Radar' advisory position staffed even though there was no traffic on that position; and none of us noticed the overtake. Many people in the Tower at that time were also still young; less experienced controllers; most I believe have 5 years or less in the agency.Having talked about this incident; I know now that I need to be extra vigilant at monitoring the scope. I have been briefed on what is expected of me as a Coordinator; but I have never had formal training where it is a certified position. The only requirement is that I be certified on Local. Perhaps formal training is necessary to show me how to perform my task of getting multiple releases at the proper times and to also watch the Radar screen; essentially showing me how to properly scan as it pertains to that position's duties.