More than 150 years separated the murders of Bridgett McCaffry and Teresa Halbach, but they may prove to be historic bookends to Wisconsin's century-and-a-half-old law preventing the execution of convicted killers.

Voters in Wisconsin will be asked in November whether the Legislature should enact the death penalty, ending America's second-longest prohibition on capital punishment.

While the vote is advisory, the outcome is awaited with great interest by partisans on both sides of the roiling capital punishment debate because votes on the death penalty usually are confined to legislative chambers and courtrooms. Referendums have been rare in the volatile public arena, where years of polls show consistently strong support for capital punishment.

The upper Midwest states have long histories of resistance to the death penalty, and the coming Wisconsin vote is the first potential crack in that fortress. If the referendum is approved, pressure will build on Wisconsin lawmakers--they effectively told voters they want their opinion--to respond to public sentiment.

"I'm certainly worried about it. I take it very seriously," said E. Michael McCann, Milwaukee County's district attorney and a longtime opponent of the death penalty.

The last execution in Wisconsin was in 1851. Nearly 3,000 people showed up in Kenosha to watch the hanging of John McCaffry, convicted of killing his wife, Bridgett. McCaffry struggled at the end of the rope for several minutes before dying, according to local reports at the time, and two years later the state outlawed the death penalty.

Through generations of occasionally horrific murders--most notably those by serial killer Jeffrey Dahmer, who killed 17 men and boys from 1978 to 1991--the state's death penalty ban has endured, in spite of repeated legislative efforts to overturn it.

Whether by coincidence of events or the persistence of death penalty advocates, official political resistance shifted after the slaying last Halloween of Teresa Halbach, a young freelance photographer. Steven Avery, who had been released from prison in 2003 after being wrongfully convicted of an assault, has been charged with Halbach's death near Manitowoc.

Avery is scheduled to go on trial Oct. 16, three weeks before the vote. The timing of the trial has provoked charges from death penalty opponents that this effort smacks of election-year politics. That charge has been dismissed by death penalty supporters, including state Sen. Alan Lasee, who has been pushing for the death penalty for 28 years.

A "number of vicious murders over the years--and one in particular," Lasee said, referring to Halbach, helped clear the way for a public vote.

"I believe a majority of Wisconsin citizens strongly support the death penalty," he said.

Polls suggest Lasee is right. A poll completed in April by the St. Norbert College Survey Center and Wisconsin Public Radio found that 61 percent of those questioned said they would vote for a referendum question similar to the one heading for the November ballot. Thirty-three percent were opposed.

A recent USA Today/Gallup Poll showed similar support nationwide--65 percent favored the death penalty for those convicted of murder. Twenty-eight percent opposed it, the poll said.

"What's happening in Wisconsin is in response to a particular crime," said Richard Dieter, executive director of the Death Penalty Information Center, a Washington advocacy group that has criticized the way capital punishment has been applied in the U.S.

"Legislators would be hard-pressed to reject the public's sentiments, but there are public policy reasons for doing so," Dieter argued, pointing to the January 2000 decision by then-Illinois Gov. George Ryan to impose a moratorium on the death penalty after an investigation by the Tribune raised questions about the fairness of how it was applied. The moratorium remains in effect.

"The death penalty used to be an easy sell," Dieter said. "Now it's a multisided issue."

Twelve states and the District of Columbia do not allow the death penalty, and in some of those places the prohibition is deeply rooted. The death penalty ban has been part of the Michigan Constitution since 1846.

Minnesota's last execution was in 1911; in Massachusetts it was 1947. Yet legislatures in each of those states--usually in response to specific murder cases--have tried recently to overturn death penalty bans.

Oregon residents have voted four times in the past century on the death penalty--twice approving it and twice rejecting it. The most recent tenure of capital punishment in the state began in the mid-1980s. A campaign to repeal the death penalty in 2002 was abandoned after polls showed overwhelming support for capital punishment.

"This is a decision that each state has to make individually, and a lot of times it depends on what's going on, [like] a particularly horrific set of murders," said Joshua Marquis, the Clatsop County, Ore., district attorney and vice president of the National District Attorneys Association. Marquis, a death penalty advocate, supports letting citizens vote on the issue.

If Wisconsin voters approve the death penalty by a margin that reflects national polls, it likely would create a new and contentious chapter in the state's death penalty politics, one influenced by an unusual entrant--a public referendum.

Keith Findley, a law professor at the University of Wisconsin-Madison and co-director of the Wisconsin Innocence Project, which provides legal assistance to inmates who say they have been wrongly convicted, said it will take a "seismic change" to overturn generations of cultural opposition to the death penalty in Wisconsin.

"We haven't had it since 1853. Certainly a lot of people want it [the death penalty], but a lot of people don't," Findley said, pointing to judges and prosecutors, such as Milwaukee County's McCann.

"This is an advisory referendum, and even if it passes, it will not mean by any stretch that we'll have it. It would still have to pass the Legislature," Findley said. "If it passes, I'm not sure what it means."

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tmjones@tribune.com