Is able to be found in prison (3)
I believe the answer is:
can
This clue is a double definition.
'is able' is the first definition.
(if you can do something, you are able to do it)
'prison' is the second definition.
(the can is American slang for prison)
'to be found in' acts as a link.
(Other definitions for can that I've seen before include "SECOND PART OF 10" , "Airtight metal container" , "(Tin) container" , "Metallic container" , "Metal container for food" .)