Adrian taps finger on his chin and replies; "True that alchemy can create the fire but it means the arsonist but enter disguised as homeless, which is likely easy, and start fire in remote location in rowhouse and depart before it grows too big. So some watch members need be inside the rowhouse check for any possible good place to start fires. Same also applies if arsonist uses magic.<br/><br/>As conjurer if I would want set a fire, I would summon a entity which may be even incorporeal and so able slide underneath street's floors and along walls of rowhouse and set things on fire rather easily. But nothing bad in placing a mage look out for case if magic use on creating fires is direct; like fireball through narrow window gap.<br/><br/>I did not suggest leaving a single alarmless sewer entrance. It's good idea place alarm spell on all of them. True that after months of kidnappings they unlikely would expect it but we better not underestimate our foe. The foe may keep checking the exits with simple as detect magic cantrip to see is there any traps or alarms in place before proceeding.<br/><br/>True that being defensive is not good, that's why I suggested our bait based trap. True that there is no guaranteed that our bait gets targeted by the kidnappers but it's better than nothing as we have no clues about the case what analyze besides maths and regularity of the acts and events. We also cannot keep eye to all homeless people who are already outside, so only choice is organize them to small groups and watched over by guards best as they can while we send our bait out and hope by Tymora's luck that the kidnappers take the bait. We have lots people here and so we can afford spread into two teams; one observe over rowhouses for arsony and other focusing pull the bait act.<br/><br/>Considering potential of magic and cultists and what not, have you considered asked aid of Khelben Blackstaff or his students?"