Why can't there be two Manks, a Mafia, and a Townie? It's not necessary for him to investigate every day.
Well... One block is clearly an investigation (yesterday's), and the other two are from Mafia and Town, or from Mank and Town, or from Mank and Mafia, and one of them cannot be a blocker. In short, Medj and Master cannot be executed now. They need to figure it out themselves tonight.
So, if Mank stole the kill and the block, he could only have used the kill, and his second action would be another investigation. If he used the block, the target should be quite specific, and such a target could very well have been present tonight. If he used the investigation, it means that the Mafia are blocked to a lesser extent.