PORTLAND — Three Brooklyn, N.Y., men and a Portland woman are in custody on drug charges following a six-month investigation by the Maine Drug Enforcement Agency that led to the seizure of $30,000 in heroin and cocaine.

Residents in the building at 638 Congress St. and others nearby had reported an unusual number of people entering and leaving an apartment. The apartment was rented by Denise Parham, 54.

Police say the apartment was being watched and that on Monday they saw a drug sale between Parham and two other people. Based on that, and the preceding investigation, Portland police and MDEA agents executed a search warrant at the apartment.

They seized 72 grams of suspected crack cocaine, 125 grams of suspected heroin and almost $2,800, police said.

Police charged Parham, Gabriel “Deacon”Williams, 28, Robert Combs, 20, and Michael Fleury, 23, with drug trafficking and they are all being held on $50,000 bail at Cumberland County Jail pending a court appearance. Williams also was charged with violating bail conditions because he had been arrested earlier on drug charges as part of the same investigation.