I must investigate you must investigate she must investigate we must investigate you must investigate they must investigate
V-ing form
I must be investigating you must be investigating she must be investigating we must be investigating you must be investigating they must be investigating
Perfect
I must have investigated you must have investigated she must have investigated we must have investigated you must have investigated they must have investigated
V-ing perfect
I must have been investigating you must have been investigating she must have been investigating we must have been investigating you must have been investigating they must have been investigating
Negation
Simple form
I mustn't investigate you mustn't investigate she mustn't investigate we mustn't investigate you mustn't investigate they mustn't investigate
V-ing form
I mustn't be investigating you mustn't be investigating she mustn't be investigating we mustn't be investigating you mustn't be investigating they mustn't be investigating
Perfect
I mustn't have investigated you mustn't have investigated she mustn't have investigated we mustn't have investigated you mustn't have investigated they mustn't have investigated
V-ing perfect
I mustn't have been investigating you mustn't have been investigating she mustn't have been investigating we mustn't have been investigating you mustn't have been investigating they mustn't have been investigating
Interrogative form
Simple form
must I investigate? must you investigate? must she investigate? must we investigate? must you investigate? must they investigate?
V-ing form
must I be investigating? must you be investigating? must she be investigating? must we be investigating? must you be investigating? must they be investigating?
Perfect
must I have investigated? must you have investigated? must she have investigated? must we have investigated? must you have investigated? must they have investigated?
V-ing perfect
must I have been investigating? must you have been investigating? must she have been investigating? must we have been investigating? must you have been investigating? must they have been investigating?
Interro-negative form
Simple form
mustn't I investigate? mustn't you investigate? mustn't she investigate? mustn't we investigate? mustn't you investigate? mustn't they investigate?
V-ing form
mustn't I be investigating? mustn't you be investigating? mustn't she be investigating? mustn't we be investigating? mustn't you be investigating? mustn't they be investigating?
Perfect
mustn't I have investigated? mustn't you have investigated? mustn't she have investigated? mustn't we have investigated? mustn't you have investigated? mustn't they have investigated?
V-ing perfect
mustn't I have been investigating? mustn't you have been investigating? mustn't she have been investigating? mustn't we have been investigating? mustn't you have been investigating? mustn't they have been investigating?