original_query: What was the reason for Mr. Boffin's attempt to murder and maintain his alias?
query: What was the reason for John Harmon's attempt to murder and maintain his alias?
answer: John Harmon (who used the alias John Rokesmith) didn't attempt murder, but he did survive an attempt on his life by Riderhood.  He maintained his alias to observe Bella Wilfer before claiming his inheritance and to see if she would love him for himself, not his wealth.