DAVENPORT, Iowa—Rand Paul expressed deep skepticism of the death penalty Thursday as he repeated his position that states should be able to decide whether to keep it.

The Kentucky senator, appearing at an afternoon book signing here, responded to a question about the neighboring state of Nebraska’s ban on capital punishment this week.

“My first thoughts aren’t that forgiving for someone who would hurt a member of my family, but I also understand there have been times when we haven’t gotten the right person,” he told reporters. “And somebody who is distrustful of big government, like I am, is also distrustful of so much power being given to government to kill somebody, when there might be a mistake. A lot of eyewitness testimony has been shown over time not to be very good.”

Paul complained that many witnesses in murder trials are not credible.

“We also have the problem of when you’ve got three thugs and they’re all testifying against each other, and two of them say, ‘Let’s say he did it,’ and the other two say, ‘Let’s say he did it,’” he said. “So your testimony is coming from people who are not necessarily the best witnesses, as far as veracity.”

The Nebraska legislature voted Wednesday to override the governor’s veto of their death penalty ban, making them the first red state to do so in decades but the seventh state since 2007.

Paul, who has said in the past that death penalty is a state issue, used his ideological support for federalism to avoid staking out a firm position.

“It’s a tough issue,” he said. “Most crimes are adjudicated at the state level and should be, so there really are almost no crimes at the federal level really under the Constitution that would require the death penalty – I think treason being one. It isn’t a big issue, I think as far as a change in federal policy, and I would leave it for the most part to the states.”

Paul did not take follow-up questions. The issue has been in the news recently in the wake of the Boston Marathon bomber being sentenced – under federal statutes, by federal prosecutors – to death. Paul did not mention the recent episodes of botched executions, another of the main reasons cited by death penalty critics.

Paul has made criminal justice reform, including the repeal of mandatory minimums, central to his presidential campaign. He spoke to a crowd of 80 here about an Iowa woman who was sentenced to more than 10 years in prison over her use of methamphetamine.

The senator’s stump speech mainly focused on his fight to let the Patriot Act sunset on Sunday at midnight.

Speaking at a minor league baseball stadium on the banks of the Mississippi River, Paul told the crowd that his voice is still raspy from speaking for nearly 11 hours on the Senate floor last week about his opposition to the law. He noted that his opposition has forced the Senate to cut short its Memorial Day recess, reconvening Sunday evening in an 11th hour effort to prevent parts of the program from expiring.

“I’m expecting a very cool reception from the other senators, but these are important debates,” he said, adding: “I don’t know if I can win or not.”

Paul also argued that he’s the most electable candidate. He said polls have shown he could beat Hillary Clinton in Colorado, Iowa, Pennsylvania and New Hampshire.

“Quinnipiac did a national poll this week…and only two Republicans, and I was one of them, beat Hillary Clinton in a nationwide poll,” he said. “So people need to ask themselves, and Republicans need to ask themselves, who can win in the fall?”

In fact, the Quinnipiac University poll he referred to showed Clinton leading Paul by 4 points, 46 percent to 42 percent, in a hypothetical matchup.