The gunman, described as a disgruntled client, had charged into the Workers' Compensation Building in downtown Edmonton armed with a rifle about 8:45 a.m. (1445 GMT) Wednesday morning, and quickly took a number of hostages in an office on the eighth floor.
Rocchio would not release the gunman's name or age. He said the man wanted a chance to tell his story.
Rocchio said a single police negotiator convinced the man to let the hostages go one by one throughout the day, with the last one being set free just half an hour before the gunman gave himself up. About 700 people work in the building on a normal day.
Emergency police dispatchers received a call from the building shortly after the man charged in and quickly brought in tactical officers and negotiators.
Don Bellerose, a neighbor in the assisted-living facility where the hostage taker apparently lived, said the man sent a text message to one of the nurses at the facility saying he was going to settle a score with the Workers' Compensation Board on Wednesday morning.
He did not disclose the hostage-takers name and estimated his age at about 35.
Bellerose said he believed the gunman was working in the concrete industry when he was injured on the job. He was cut off from benefits and had threatened to jump off a bridge into the North Saskatchewan River about three months ago. Bellerose said the bridge was shut down for three hours.
He also said the man's wife was taking him to court to get custody of their children.
Workers' Compensation Board President and CEO Guy Kerr said in a statement that their focus and priority now and in the coming days will on their employees and helping them to cope with the traumatic experience. He also thanked police.
In 1993, an armed man claiming unfair treatment from Alberta's Workers' Compensation Board took three hostages before eventually surrounding. Another man killed himself in the parking lot of a Calgary WCB building two years earlier. The death led to a public inquiry and a government apology.
Associated Press writer Rob Gillies in Toronto contributed to this report.