Officers were called on Saturday night with concerns for the welfare of two men at an address on Wellesley Road following reports of an altercation.
Two men were found dead inside the property and the body of a third man outside the property.
A 32-year-old man from Colchester has been arrested on suspicion of murder.
Detectives are not looking for anyone else in connection with the incident, but are keeping an open mind.
Wellesley Road remains closed while police enquiries continue.
Anyone with information should contact our Major Crime Team on 101 quoting incident 1400 of 5 October or email firstname.lastname@example.org.