A day after two sex offenders were found shot to death in separate towns in Maine and a suspect killed himself on a bus in Boston, investigators said Monday they still didn't know how or if the three men were connected.

"We don't have a link, we don't have a connection, and we have really more questions than we have answers as to what sparked this violence," Maine Public Safety Department spokesman Stephen McCausland said Monday.

Joseph L. Gray, 57, of Milo, Maine, and William Elliott, 24, of Corinth, both registered sex offenders, were found shot to death Sunday in their towns, 25 miles apart, police said.

A man identified by police as Stephen A. Marshall,20, was seen driving away from the scene of Elliott's shooting. Police did not know if Marshall knew either of the shooting victims.

Almost 12 hours later, police pulled over a bus from Maine approaching Boston's South Station. As officers boarded the bus, Marshall pulled out a .45-caliber handgun and shot himself in the head, said David Procopio, spokesman for the Suffolk County district attorney.

Maine State Police were calling Marshall a "person of interest" in the slayings of the two men and had told Boston authorities that he may be heading toward the city, McCausland said.

No one else on the bus was injured, Procopio said. Five passengers were examined because they were splattered with blood.

Marshall, who lived in Cape Breton, Nova Scotia, had come to Houlton, Maine, for the first time to meet his father, McCausland said.

Marshall had been driving his father's pickup, but the father hadn't realized his son and truck were missing, McCausland said. Marshall also took two handguns and a rifle from his father, the spokesman said.

Gray's name was posted on a state Web site because he had moved to Maine after a Massachusetts conviction for sexual assault on a child under 14, McCausland said. Elliott's conviction was for having sex with a girl who was under the legal age, he said.

After the killings, Maine State Police removed a list of 2,200 sex offenders from the Web site as a precaution, McCausland said.

"It will go back on line, absolutely," he said.

All states have sex offender registries and almost all of them post the information on line, according to Blake Harrison of the National Conference of State Legislatures.

Maine's Web site contained offenders' names, addresses, identifying characteristics and place of employment, as well as photographs.

A sex offender registry Web site in Washington state was cited in the deaths of two convicted child rapists last summer. Michael Anthony Mullen, 35, said he targeted the pair after finding them on Whatcom County's online list. He pleaded guilty to two counts of second-degree murder and was sentenced to more than 44 years in prison.