Double-crosser noun – One who betrays a trust or an allegiance. Stoolie and double-crosser are semantically related In some cases you can use "Stoolie" instead a noun phrase "Double-crosser".
Stoolie noun – A person who provides information about another's wrongdoing. Double-crosser and stoolie are semantically related in informer topic. Sometimes you can use "Double-crosser" instead a noun "Stoolie".