A team of 65 officers from the Kent and Essex Serious Crime Directorate carried out raids at addresses in Colchester and Clacton, Essex police said in a news release.
"Over the past seven months my officers have been investigating a series of cases which appear to be the work of an organized crime group taking advantage of the elderly and vulnerable and exploiting them for criminal gain," Assistant Chief Constable Gary Beautridge said.
The investigation involved video surveillance of elderly people withdrawing large sums of money from banks accompanied by some of the suspects, The Guardian reported.
The victims were conned into paying large sums for unnecessary work on their homes or overcharged for work that was done. Some were persuaded into loaning money to gang members.
Eighteen of the victims, predominantly widowed or unmarried women, died during the investigation, police said.