Fill in the blanks with either of the words guilty or suspect

There are two sentences:

Police believe my neighbor robbed a bank.He is a/an ..........

She stole the money.She was......... of the crime.

I think for firat sentence we should use "guilty" and for second one "suspect". Because suspect of the crime make more sense than guilty of the crime.but I am not sure. On the other hand I think we use suspect when we are not sure who is the criminal.In the first sentence if the word 'believe' means polices are not completely sure the answer to first one should be suspect and second one guilty.

@Kate Bunting from the comments already did a good job clarifying your confusions, so I will just provide extra validation.

From your first sentence, I see that before the blank there is a determiner, the "a/an"; only "suspect" would fit here, and uses determiner "a"; "suspect" is a noun, and that is what the blank would require, since a noun is marked by a determiner, and not the adjective "guilty."

The second sentence, on the other hand, has "She was" before the blank, and "suspect" certainly would not fit here, at least, not in correct English ("she was suspect" is broken and just unnatural English). "Guilty" has to be used here by default, since it is an adjective, and that can be used to describe what someone was from before.