must investigate
Regular verb: investigate - investigated- investigated

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I must investigate
you must investigate
he must investigate
we must investigate
you must investigate
they must investigate 	I must be investigating
you must be investigating
he must be investigating
we must be investigating
you must be investigating
they must be investigating	I must have investigated
you must have investigated
he must have investigated
we must have investigated
you must have investigated
they must have investigated	I must have been investigating
you must have been investigating
he must have been investigating
we must have been investigating
you must have been investigating
they must have been investigating	

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

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