I always thought about a game type when town investigatives could communicate to eachother in a way. When the games are custom with random town or town investigative then there is a lot of deception going on ( everybody claiming invests, lookouts, sheriffs etc. ) My suggestion is to add a something called 'Evidence Box'. Evidence box would get content when two different town investigative roles investigate the same crime. For instance, person A kills person B . Sheriff interrogated person A and found out that he is a member of the mafia, but he doesn't know if the person is framed. At the same time, Lookout visited person B and saw two persons visit him that night, one of which is person A . Normally, sheriff would have to double check to try to remove the possibility of framing, and lookout wouldn't know which of these two persons is mafia without saying out loud who visited person B, thus revealing his role and becoming a target.
In the ' Evidence Box' scenario, both Sheriff and Lookout would get the message ' there are some evidence for you to look at' and they could read it next to the last will and death note by night - saying ' Person A is a member of the mafia and killed Person B. Next day both lookout and sheriff would know who is the guilty person without having to check them twice or reveal their roles. Also, they could use their night ability to check someone else.
In the same way I would combine Investigator and Sheriff - revealing a persons exact role, Lookout and Spy - who visited who etc. To get something into evidence box, the both investigatives would have to invest the same person/crime same day.
What do you think?