Sajib is guilty ____ murder.

Sajib is guilty "of" murder.

In English, the preposition "of" is used after the word "guilty" to denote responsibility or blame for a specific offense or crime. The structure is "guilty of [something]."

The other prepositions are not correct in this context:

• "at" is not typically used to indicate a connection between "guilty" and a crime or misdeed.

• "in" does not fit the standard grammatical structure with "guilty."

• "to" is also inappropriate in this context, as it does not convey the correct relationship between being guilty and the crime.