How Al has been involved in the investigation:
-got recruited and brought on a level with the other members ('Note to Dr. Baker...' and 'You're hereby invited to... (Baker)')
-attended meeting and contributed to a plan ('Party Crashers Inc.')
-participated in the execution of the first step of said plan ('Stakeout')
How his contribution will continue
He will continue keeping an eye on the building in question and further get as much information as possible about the leaflet lackey (by shadowing him as well as possible) planning to have him captured and questioned.