Hmm, level 1 party, no Clerics? And presumably no Druids, since they can heal too. And no Psions, because Concussion is the perfect spell for this sort of thing.
I think you'll still have a problem, because at level 1 your players feel vulnerable and have no real escape options (especially with low magic). Your players might be different, but in all the campaigns I've been in imprisonment is viewed as Not A Good Thing, the sort of thing to be resisted at all costs, especially if it's something the players know they're innocent of. Which means the players might resist with physical force (lethal, that is) which has long-lasting consequences.
All I was trying to say is that if the guards are level 1 also, they'd bring 30 or more men at once to ensure they win with no losses (or better yet, you surrender without a fight). If you're in the Army, when clearing a house you send in 20-30 men to ensure no casualties.
Now, if you were in a town where weapons were all peace-bonded on entry, this'd be a different thing. But, if the party is known to be armed, the guards wouldn't take chances, especially if the guards are only level 1 themselves and (presumably) have comparable equipment.
It all comes down, IMHO, to whether you WANT the players to resist. If no, send a lot more guards. If yes, realize that there's a good chance someone will die, and that most towns won't forgive cop-killers.
(Presumably you're running a town so corrupt that the guards will imprison people with no evidence on the word of an aristocrat? Or was the evidence faked, in which case the players might not get out of it to do the other job?)