Media playback is unsupported on your device Media caption Relatives of Stephen Port's victims want to know why no officer has been interviewed about failings in the investigation

Families of victims of a serial killer are appalled at the inquiry into police failings associated with the case.

Stephen Port, 42, was sentenced to life imprisonment in November 2016 after being found guilty of four murders.

The Independent Police Complaints Commission (IPCC) said it has compiled 7,000 pages of material on the case, and is committed to finding answers.

But victims' relatives are dismayed that none of the police officers under investigation have been interviewed.

Between June 2014 and September 2015, Port murdered Anthony Walgate, 23, originally from Hull, Gabriel Kovari, 22, from Lewisham, south-east London, Daniel Whitworth, 21, from Gravesend, Kent, and Jack Taylor, 25, from Dagenham, east London.

The first victim - Anthony Walgate - was found outside Port's flat and the other three either in or next to a churchyard 500m (1,640ft) away.

The deaths were not initially treated as murders and detectives missed a string of chances to catch the killer, including accepting Port's lies after he was arrested in connection to the first killing, believing a fake suicide note that Port planted on Mr Whitworth, and ignoring family and friends of the victims who urged them to link the deaths.

Image copyright Met Police Image caption Daniel Whitworth (left) was murdered a year before Jack Taylor (right) died

Mr Taylor's sisters - Donna and Jenny - told the BBC they feel like they are being ignored once more.

Donna Taylor said: "We had to fight for the police to listen and now we're having to do the same for the IPCC."

Jenny Taylor said: "It's heartbreaking as it's like it's happening all over again.

"We shouldn't have to keep chasing things up after everything that we've been through."

Mandy Pearson, stepmother of Mr Whitworth, said: "We continue to seek answers and accountability from the police about how, for a whole year, they let us believe that Daniel had committed suicide, in which time Port went on to kill again.

"We really did hope that, with Port now behind bars, the police would be held to account for their actions. The fact that after all this time we're still no further forward is insulting and distressing for all of the families."

Media playback is unsupported on your device Media caption The BBC's Daniel Sandford reports on the crimes of Stephen Port, "a serial rapist who became a serial killer"

The families are also frustrated that the IPCC has not interviewed any of the 17 police officers under investigation despite earlier assurances.

The families were initially told the interviews would occur at the start of the year, and in March - following pressure by the families - the IPCC announced its investigation was moving into the "interview phase."

Mr Walgate's mother, Sarah Sak, told the BBC she was "shocked and appalled" at the progress of the investigation.

She said the IPCC was not updating the families on the inquiry's progress despite promising to do so.

"The first time they [the IPCC] met us they said we'd get an update - a monthly update - and we've never had one yet. There's no communication, nothing."

"It is very, very frustrating because I thought the IPCC would be totally independent, would be more professional, and a lot faster than they have been."

She said the families think the police officers and their lawyers are "calling the shots where it should be the IPCC doing that."

Image copyright Met Police Image caption Anthony Walgate (left) and Gabriel Kovari were Port's first victims

The families' lawyer, Neil Hudgell said: "[We are] losing confidence that the IPCC has the ability to get to the truth; the longer this drags on, the greater the chance of evidence being lost or forgotten."

IPCC commissioner Cindy Butts said: "Since Stephen Port was convicted we have undertaken a rigorous process of pre-interview disclosure.

"In total this has amounted to over 7,000 pages of material which we have provided to representatives for the 17 officers."

She thanked the victims' families for their information and insight, and added the IPCC was "committed to providing them with answers to their questions and concerns, and will do so as soon as it can."

The Metropolitan Police has admitted it missed "potential opportunities" in investigating the deaths.

Port was apprehended after the case was passed from detectives in Barking and Dagenham to the Met's main homicide command.

The successful investigation into Port's crimes is not part of the IPCC inquiry and the families have praised the detectives involved.