could preinvestigate
Regular verb: preinvestigate - preinvestigated- preinvestigated

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could preinvestigate
you could preinvestigate
he could preinvestigate
we could preinvestigate
you could preinvestigate
they could preinvestigate 	I could be preinvestigating
you could be preinvestigating
he could be preinvestigating
we could be preinvestigating
you could be preinvestigating
they could be preinvestigating	I could have preinvestigated
you could have preinvestigated
he could have preinvestigated
we could have preinvestigated
you could have preinvestigated
they could have preinvestigated	I could have been preinvestigating
you could have been preinvestigating
he could have been preinvestigating
we could have been preinvestigating
you could have been preinvestigating
they could have been preinvestigating	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't preinvestigate
you couldn't preinvestigate
he couldn't preinvestigate
we couldn't preinvestigate
you couldn't preinvestigate
they couldn't preinvestigate 	I couldn't be preinvestigating
you couldn't be preinvestigating
he couldn't be preinvestigating
we couldn't be preinvestigating
you couldn't be preinvestigating
they couldn't be preinvestigating	I couldn't have preinvestigated
you couldn't have preinvestigated
he couldn't have preinvestigated
we couldn't have preinvestigated
you couldn't have preinvestigated
they couldn't have preinvestigated	I couldn't have been preinvestigating
you couldn't have been preinvestigating
he couldn't have been preinvestigating
we couldn't have been preinvestigating
you couldn't have been preinvestigating
they couldn't have been preinvestigating	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I preinvestigate?
could you preinvestigate?
could he preinvestigate?
could we preinvestigate?
could you preinvestigate?
could they preinvestigate? 	could I be preinvestigating?
could you be preinvestigating?
could he be preinvestigating?
could we be preinvestigating?
could you be preinvestigating?
could they be preinvestigating? 	could I have preinvestigated?
could you have preinvestigated?
could he have preinvestigated?
could we have preinvestigated?
could you have preinvestigated?
could they have preinvestigated? 	could I have been preinvestigating?
could you have been preinvestigating?
could he have been preinvestigating?
could we have been preinvestigating?
could you have been preinvestigating?
could they have been preinvestigating? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I preinvestigate?
couldn't you preinvestigate?
couldn't he preinvestigate?
couldn't we preinvestigate?
couldn't you preinvestigate?
couldn't they preinvestigate? 	couldn't I be preinvestigating?
couldn't you be preinvestigating?
couldn't he be preinvestigating?
couldn't we be preinvestigating?
couldn't you be preinvestigating?
couldn't they be preinvestigating? 	couldn't I have preinvestigated?
couldn't you have preinvestigated?
couldn't he have preinvestigated?
couldn't we have preinvestigated?
couldn't you have preinvestigated?
couldn't they have preinvestigated? 	couldn't I have been preinvestigating?
couldn't you have been preinvestigating?
couldn't he have been preinvestigating?
couldn't we have been preinvestigating?
couldn't you have been preinvestigating?
couldn't they have been preinvestigating?