Police officers who were present on the day of the Hillsborough disaster are refusing to co-operate with an investigation into an alleged cover-up, it has been claimed.
Lord Falconer, who has been advising the victims' families, told MPs that "significant numbers" of officers are either claiming that they are sick, or are refusing to speak to a police watchdog because they have retired.
Giving evidence to the Home Affairs Select Committee alongside members of the Hillsborough Family Support Group, he said: "If you're just a witness, which is the way they've initially been approached, do you have an obligation to co-operate if you're a police officer in helping to get to the truth of an incident like this?"
He said he was surprised at the number of officers not willing to give evidence. Retired officers are not obliged to speak to the watchdog, the Independent Police Complaints Commission, which is carrying out the inquiry.
The IPCC said 13 officers out of 250 have declined to be interviewed, and another 12 have been classed as unfit to give evidence.
The peer, a former Lord Chancellor, added: "The numbers suggest that there are some people who are just not co-operating."
Representatives of relatives of the 96 people who were killed in the disaster in 1989 were called to speak to the committee ahead of fresh inquests into their loved ones' deaths next week.
Margaret Aspinall, from the Hillsborough Family Support Group, said she is concerned about the number of officers who say they are too sick to give evidence to the IPCC.
She said: " It's very important they should be brought up to answer questions. A lot of the families, if you look back over the 25 years, a lot of the families are sick and old, but they've still got to go through this procedure to get to the truth and I think there's no difference for them (police officers) as well, they should do exactly what the families have done.
"Over the past 25 years now we've lost an awful lot of families who've not seen this through, who were desperate to see this through, and I think... that they (police officers) should be made to be brought forward to answer any questions relating to Hillsborough because that's they only way we will get the truth."
Sheila Coleman, from the Hillsborough Justice Campaign, also gave evidence, and called on Home Secretary Theresa May to investigate claims that family groups were put under surveillance.
She wants the allegations examined alongside claims that the family of murdered Stephen Lawrence was spied on by undercover officers, and that an officer accused of corruption had links to the failed investigation into the death of private investigator Daniel Morgan.
Britain's worst sporting disaster unfolded at Sheffield's Hillsborough stadium on April 15 1989 during Liverpool's FA Cup semi-final against Nottingham Forest as thousands of fans were crushed in the ground's Leppings Lane terrace.
In December 2012, verdicts of accidental death from the original inquest in March 1991 were quashed.
The action was taken after the Hillsborough Independent Panel studied thousands of documents and reported that there had been a huge cover-up of what happened at Hillsborough and its aftermath.
Ms Aspinall said that she is hoping that the inquests, expected to take several months, will be "thorough and open".
"The expectation is that it's a thorough inquest on all of the deceased who died that day. The most important thing is we have a thorough and proper examination of every individual who died that day. And as long as it's thorough and open, that's important for all the families."