What does "found in" mean?
This was from the next sentences: "He knew he had to keep searching until he found a sympathetic person. Roberts found one in Dr. Henry Bruyn."

Question

Answer

He knew he must search or look for a sympathetic person.  He had to search to find this person.  When he met Dr. Bruyn, he found one (the sympathetic person).  One in this case is a pronoun which refers back to the previous "sympathetic person". 
 "Found (one) in"  means that  the sympathetic person that he needed was "found in" the character or personality of Dr. Bruhn".

Answer

He found the sympathetic person he was searching for ... it was Dr Bruyn.  This is a phrasal verb