Can your landlord let the police in your apartment if they do not have a warrant?
My fiancée was in his and his brother's apartment along with myself. His brother was not home so we did not answer the door for the police. After about a hour of knocking the landlord let them in even though his brother was not around. They arrested my fiancée because of domestic violence against his ex wife. All that happened is they got into an argument and she called the police and said he hit her. Is any of this illegal?
As a general rule, the police can obtain consent to search from anyone with control over the property; specifically the one in charge of an area has the power to give permission to the police to search that area. Accordingly, someone who has a key or whose name appears on the lease, can legally consent to a search of the property if no one else is present. And if the property is a rental, be advised that a landlord can also let the police in. However, a landlord cannot give permission to the police to search your apartment; only places like the common areas (e.g. a washer/dryer room in an apartment building).
Note: You should keep in mind that it is not an illegal search and seizure if the police search your apartment without any permission if they feel that the search is an emergency ("exigent circumsatances").