POLICE have admitted spying on the family of Christopher Alder after he died in custody.
Humberside Police have found evidence the force placed Mr Alder's sister Janet and another person under surveillance.
The Independent Police Complaints Commission (IPCC) will now examine whether it amounted to improper conduct.
Miss Alder said the force's admission confirmed what she has long suspected.
She said: "From day one, I have believed they were following me and I have always said that. I have had to deal with people thinking I had lost the plot, but this confirms my suspicions were right.
"I have been looking over my shoulder, scared stiff, for years. I am the victim here, why were they following me? My brother had died and I was a grieving sister.
"I am disgusted. I think just the fact I was under surveillance is improper."
Mr Alder, 37, died in the custody suite in Queens Gardens police station in 1998. An inquest later ruled he had been unlawfully killed.
A separate police investigation was launched in 2011 after his body was found in Hull's mortuary 11 years after he was believed to have been buried.
The evidence of surveillance came to light after all police forces were asked to check their records following claims the Metropolitan Police spied on the family of murdered teenager Stephen Lawrence.
Miss Alder said she hopes the new investigation will uncover who authorised the surveillance and why.
"I do welcome this investigation and I hope we finally get the truth out of it," she said.
"I want to know who it was that gave permission to do this, why they were doing it and what they found out and I want those responsible to be held accountable."
The IPCC said Humberside Police referred itself to the watchdog to assess whether a separate investigation was justified.
A spokesman said: "This follows a referral by Humberside Police, following a request from the Home Secretary that all police forces check their records for evidence of surveillance relating to the investigation into the 1993 murder of Stephen Lawrence and the Macpherson Inquiry into his death.
"Humberside Police did not discover any such evidence but their searches revealed evidence of surveillance into Ms Alder and another person.
"The IPCC will be carrying out an independent investigation into these allegations."
Miss Alder and the other person placed under surveillance will now meet with the IPCC commissioner for Humberside, Cindy Butts, to discuss the inquiry.
A spokesman for Humberside Police said: "Following an internal review, conducted in the light of interest in covert policing tactics, Humberside Police has chosen to refer to the IPCC an operation conducted a number of years ago.
"This means that Humberside Police will be unable to comment further until such time as the IPCC has concluded an investigation."
