best ways to fight roaches

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to make a long story short, i had tenants move out the week before i bought the building and they lived in filth..even my contractors didn't want to go in there, it smelt so bad..there were roaches everywhere. i had a guy come in and spray..twice the roaches are going into the adjacent apartments due to the spray, bait, and the fact that the food source is gone since the tenants are gone. i have one very clean OCD tenant who i don't want to lose that is planning on moving out bc some of the roaches are moving into his apartment through the walls...do yall know of the best roach killer? these bastards are resilient, and even if you kill them, there's babies in the walls, meaning i'll have to kill another generation of them...hoping you guys might know a 'little known' trick or something..any ideas??