Police say a file is now being prepared for the Public Prosecution Service.
The body of Ms McCausland, who was 23,  was found beside a stream in Forthriver on 8 March 1987.
The PSNI re-opened the investigation into her murder last November. She was last seen alive in a loyalist club at Tyndale.
Police believe 23-year-old Ms McCausland, who had been on a night out, was raped in the club before she was "savagely beaten" and her body dumped.
On Thursday, a 54-year-old and a 56-year-old were arrested in Belfast while two men, aged 53 and 59, were arrested in Antrim.
It followed the arrests of two men, aged 49 and 56, in Scotland and a 53-year-old man in England on Wednesday.
Fourteen people were arrested during the original investigation but no-one was charged.
Detectives conducted 29 searches and took more than 100 witness statements.
Lorraine McCausland's son, who was aged just two, when she was killed, was himself murdered 18 years later, in July 2005.
Craig McCausland died after being shot in Dhu Varren Park in north Belfast and the killing was blamed on tensions within loyalism.
Seven men arrested over the rape and murder of Lorraine McCausland in Belfast 30 years ago have been released.