One way to do it would be to add a second "if" inside the "Then" for the first flag.
So the script would look like:
If [object has flag] [object] [man] [flag name] [murderer]
- Then: If [object has flag] [object] [man] [flag name] [killer]
- - Then: ...
Alternatively, if you change the first drop-down to "expression", you'll see the generated expression for "object has flag". It looks like this:
GetBoolean(man, "murderer")
You can simply add the word "and" followed by another condition, for example:
GetBoolean(man, "murderer") and GetBoolean(man, "killer")