Sir Jeffrey Donaldson has said there must be a "comprehensive and proportionate approach" to dealing with the past.
The DUP MP was speaking after the Supreme Court ruled against the family of Belfast solicitor Pat Finucane over the decision not to hold a public inquiry into his 1989 killing by loyalists.
"The Finucane family's challenge over the decision not to hold a public inquiry was rejected clearly," he said.
"The court did find failings in the de Silva review but it must be borne in mind that an offer to hold a public inquiry under the Inquiries Act was rejected by the Finucane family.
"Under the current legacy process there are countless families who have seen no effective investigation or review into the brutal murder of their loved ones.
"Indeed for many of those murdered by terrorists there are individuals who hold information but they prefer to hide behind a 'code of honour' to their illegal criminal gangs rather than assist victims."
Ulster Unionist MLA Doug Beattie said it must be remembered that Mr Finucane was only one of more than 3,000 people who lost their lives in the Troubles and left behind grieving families.
"Like many others, the Finucane family want to know why their loved one was targeted and murdered. This same feeling is shared by the families of the police officers, soldiers and civilians who were murdered or maimed by terrorists," he said.
"We must never forget the brutality of the IRA murder gangs and loyalist terrorists."