A former U.S. attorney and Republican congressman is warning that mandatory minimum sentences can create unfairness in the justice system.

Asa Hutchinson, who is now part of a group of conservatives who want to re-evaluate "tough on crime" policies based on fairness and cost to taxpayers, told the House of Commons public safety committee Thursday that the United States made a number of mistakes and he hopes Canada can learn from them.

"When you talk about mandatory minimums, it created a lot of unfairness in our sentencing. There [were] instances of someone being peripherally involved... getting hit with a mandatory minimum, getting 10 years or more in prison, so we created escape valves... [that] gave the judge more discretion to avoid a mandatory minimum when it created unfairness. So we had to do some legislative fixes," said Hutchinson, of Right on Crime.

Hutchinson, who was also appointed to the U.S. Drug Enforcement Administration, said longer sentences in the U.S. did lead to lower crime rates.

"Well, the crime rate's gone down in the United States. And I would probably argue that the increased incarceration rate's had a positive impact on reducing the crime rate," he said.

The public safety committee is examining the costs of expanding prisons under the government's "tough on crime" agenda.

The Conservative government has introduced legislation to bring in mandatory minimum sentences for impaired driving, serious gun offences, sexual offences against children, white collar crime and drug crime, as well as legislation ending early parole for some offences.

Ian Lee, a Carleton University professor and expert in government budgets, says it's important to distinguish between violent and non-violent offenders, because it is expensive to lock-up anyone who commits a crime.

"I think there is very strong support...for incarcerating people that are violent, who are willing to commit murder or rape or sexual assault, as it's now called, because that's considered absolutely unacceptable, no excuse, full stop," he said.

"And so we incarcerate violent people, but we should not be incarcerating non-violent people because the return on investment is terrible."

The opposition parties complain the government won't tell them how much their anti-crime agenda will cost. They say building new prisons will cost too much money and that it should be spent on other policy initiatives like health.

A spokeswoman for Justice Minister Rob Nicholson said mandatory minimums shouldn't be viewed in isolation, but as a tool available to legislators. She said it's equally important for victims of non-violent crimes to feel their concerns are dealt with.

"Canadians lose faith in the criminal justice system when they feel that the punishment does not fit the crime," Pamela Stephens wrote in an email.

"Is it fair to victims of crime, or society at large, when offenders receive sentences that do not adequately reflect the serious nature of the crimes?"