LARGO — The Pinellas County Domestic Violence Task Force recorded 13 homicide cases in 2012 — the highest number the group has logged over the nearly two decades it has collected data.Eighteen people died, because five of the homicide cases were murder-suicides — also an unusually high number in a county that typically sees only one or two a year. The statistics frustrate task force members, who have no idea what caused the sudden spike, said Frieda Widera, chairwoman of the fatality review subcommittee.It could take as long as six years to figure out the reason for the increase, because task force policy is to study cases after they've been cleared by the criminal justice system, when police and prosecutors are more willing to share details that might otherwise jeopardize prosecution.The task force also gathers information from the county health department, clerk of court, domestic violence centers, probation officers and legal aid, among others."Behavior is hard to predict and, with domestic homicide, we're always trying to look at the past to prepare for the future," said Widera, a victim advocate at the Largo Police Department. "But sometimes it takes years upon years of data to see a significant trend."The statistics are included in the most recent study by the Pinellas task force, which has tracked trends in 114 fatal domestic violence cases countywide since 1996. Until last year, Widera said, the highest number of domestic-related homicide cases was 10, recorded in 2001.Among 2012's Pinellas killings, as described by authorities: • Sharon Byrd, 46, in September stabbed her 44-year-old husband, Russell, in their St. Petersburg apartment after he answered a phone call from another woman, police said.• According to reports, Eugene Agbebaku, 33, shot his 32-year-old estranged wife, Ingrid, and himself in Clearwater, where she and their children were staying with a relative. The couple had been scheduled to appear in divorce court the day of the June 5 shootings.• In April, authorities said, James Wolski, 35, of Largo turned the gun on himself after shooting to death his 40-year-old wife, Stacie, in a Walgreens parking lot, orphaning the two paramedics' 4-year-old daughter.• In August, police accused Luis Antonio Santiago, 48, of running over his 36-year-old girlfriend, Belinda Joyce Thomas, as she fled their Pinellas Park home. Thomas' elementary school-age children witnessed her death. All five of the Pinellas murder-suicides in 2012 were committed by males, police said. At least two of the couples were in the process of divorce. In two other cases, baffled loved ones told reporters they saw no warning signs.The domestic violence report shows that drugs or alcohol played a role in 74 percent of the 114 cases. In 42 percent of cases, the perpetrator had been previously arrested for domestic violence, yet a judge had ordered batterer intervention in only 25 percent of cases.But most disturbing, the task force says, is that in 70 percent of cases, friends, family, co-workers or neighbors knew about the relationship's violent nature, yet did nothing."For this report, we tried to make it much more user friendly … and give the individual person in the community specific ideas on what they can do," Widera said. "When somebody is telling you something is happening, believe it's happening, be willing to act, and know the resources to give the individual."Keyonna Summers can be reached at (727) 445-4153, [email protected] or on Twitter @KeyonnaSummers.