BOSTON (CBS/AP) — Five people have been arrested in connection with trafficking women for sex at brothels in and around Boston.

The arrests were made Thursday after a four-month joint operation by local police, the FBI, the Massachusetts State Police, and Massachusetts Attorney General Maura Healey’s office.

The brothels were in Boston, Cambridge, North Reading and Quincy and prosecutors say the suspects were using the web site BackPage.com to advertise for sex.

Pingxia Fan, 40 of Boston, Timothy Hayes, 50 of Gloucester, Simon Shimao Lin, 59 of Boston, Biqun Xiao, 47 of Deerfield, N.H., and Robert Mozer, 65 of Deerfield, N.H. were arrested Thursday for trafficking women for sex at brothels in Boston, Cambridge, North Reading and Quincy.

Prosecutor: 4 defendants kept prostitutes against their will to perform sex 12 hrs per day. Women came from NYC pic.twitter.com/AEkZLQ3Yzt — David Robichaud (@RobiWBZ) May 4, 2017

Prosecutors allege that the suspects were making at least $100,000 each week and brought in as much as $5,000,000 each year.

The women were held allegedly held against their will and spoke only minimal English. They were also forced to work for 12 hours each day.

Prosecutors wanted over $1,000,000 bail for each suspect.

The judge set bail at $150,000 for three of the suspects. The others are being held for $50,000 bail.

(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)