BANGOR – With Stephen Marshall still at large and police uncertain whether he would strike again, Bangor investigators beefed up local patrols Sunday and searched a wooded area with a dog.

But the real clue to Marshall’s whereabouts came from a small bathroom in a downtown bus terminal.

A plastic bag with unspent .22 caliber bullets was found in the water tank of a toilet.

The bag kept the stopper open and the water flowing, prompting the bus station lead agent, Peter Brountas, to become curious about the toilet, to lift the lid and pull out the obstruction late Sunday evening.

Surprised to find bullets, Brountas, who has worked at the station for 40 years, carefully placed the bag down and called police.

Marshall, 20, who shot and killed two sex offenders Sunday – one in Milo and the other in Corinth – had taken three guns from his father’s home in Houlton, including a .22 caliber pistol he had with him when he shot himself Sunday night on a Bangor-to-Boston bus.

Transit police honed in on the Vermont Transit Co. bus as it was arriving in Boston about 7:25 p.m., and Marshall shot himself in the head.

Earlier Sunday, investigators had been to the Bangor Bus Terminal, on the corner of Union and Main streets, several times during the day; first to drop off a name and description of Marshall and later in the afternoon, to drop off a picture of the young man.

In between visits, Marshall, 20, slipped largely unnoticed onto a bus headed south to Boston.

Marshall used an assumed name to buy a ticket for the bus to Boston, which left at 1:45 p.m. The picture provided by police looked somewhat familiar to the ticket clerk, but not enough for it to register as the man who had bought a ticket earlier in the day, Brountas said.

“She vaguely remembered him,” he said.

Most businesses downtown were closed Easter Sunday, so few if any people would have seen Marshall in the downtown. Earlier in the day, he had abandoned the silver truck he took from his father at the Sawyer Arena.

One woman, who lives in the same building in which the bus station and the Tavern, the bar next door, are located, said she noticed Marshall sitting in the terminal in one of the three black seats that comes equipped with a small pay-per-view television.

She had gone to get her mail at the terminal desk sometime between 11:30 a.m. when one bus left and 1:45 p.m. when Marshall’s bus left.

The woman, who did not want to be identified, said she wouldn’t normally have given him a second look, but he seemed familiar.

“I wouldn’t have noticed him if he didn’t look like someone I know,” she said Monday afternoon, sitting on a barstool at The Tavern.

With Marshall’s location unknown for much of Sunday, authorities increased their efforts to search the area for the man.

Bangor Detective Sgt. Paul Kenison said there was concern Marshall may strike again in the area. Four detectives were called in Sunday to alert by phone or in person as many of the estimated 100 Bangor residents listed on the state sex offender registry.

“We were just trying to be proactive, in case,” Kenison said.

Bangor police beefed up its patrol, bringing in three officers hours earlier on Sunday to add to the five officers already on the streets, Lt. Jeff Millard said Monday.

Bangor police, still uncertain of his whereabouts, searched the wooded area by Sawyer Arena, where Marshall’s pickup truck was found, about 7 p.m. Sunday. Police wanted to make sure Marshall hadn’t made his way into the woods to end his life, Millard said.

Chris Andreasson, general manager of Vermont Transit Co., said Monday from his Burlington, Vt., office, that he could remember only one other shooting-related incident on a company bus in the 32 years he has been working for the company, and that was in the 1970s, he said. Andreasson called it an unfortunate incident.

“These are few and far between, thank God,” he said.