Dragonblade
Adventurer
Absolutely a paladin could be an assassin. There would be certain things he couldn't do. He couldn't indiscriminately kill innocent people who got in his way or anything, but there is nothing in the paladin code that prohibits a paladin from using stealth to sneak into some evil lord's manor, slit his throat in his sleep and sneak out again.
The paladin's targets are determined by his church and his god. If the church has decreed their death for their crimes then the paladin will seek them out and kill them.
There is no requirement for the paladin to face them or allow them any opportunity to defend themself. Perhaps in your campaign world that may be the case or perhaps specific paladin orders may have codes that prohibit such paladin behavior.
But there is nothing specific in the PHB that prevents a paladin from operating as a ruthless harbinger of justice. He shall avoid lies and shall not use poison. But otherwise he is free to ambush, sneak, and assassinate evil doers to the best of his ability.
The paladin's targets are determined by his church and his god. If the church has decreed their death for their crimes then the paladin will seek them out and kill them.
There is no requirement for the paladin to face them or allow them any opportunity to defend themself. Perhaps in your campaign world that may be the case or perhaps specific paladin orders may have codes that prohibit such paladin behavior.
But there is nothing specific in the PHB that prevents a paladin from operating as a ruthless harbinger of justice. He shall avoid lies and shall not use poison. But otherwise he is free to ambush, sneak, and assassinate evil doers to the best of his ability.