"You need to come outside now with nothing in your hands. Your hands in the air," police shouted through a megaphone outside the home owned by suspect Robert Card's relative near the town of Bowdoin.
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SEE ALSO: Heavily armed police surrounded home in search for suspect in the fatal shooting of 18 in Maine
Dozens of law enforcement officials had descended on the property, with extended announcements calling for Card and anyone in the home to come out into the driveway. In most instances when police execute warrants - even for suspects wanted for violent crimes - they move quickly to enter the home.
"The announcements that are being heard over a loudspeaker are standard search warrant announcements when executing a warrant to ensure the safety of all involved," state police spokesperson Shannon Moss said. "It is unknown whether Robert Card is in any of the homes law enforcement will search."
As of Thursday night, Card remained at large.
Hundreds of law enforcement agents, including dozens of FBI agents, have been hunting for Card, a 40-year-old reservist with a history of mental health issues, since Wednesday night's shootings at a bowling alley and a bar that sent panicked patrons scrambling under tables and behind bowling pins and gripped the entire state of Maine in fear.
Schools, doctor's offices and grocery stores closed and people stayed behind locked doors in cities as far away as 50 miles from the scenes of Wednesday night's shootings in Lewiston.
Maine officials provide update on deadly mass shooting
Former FBI agent JJ Klaver provided some insight on the search.
SEE ALSO: What we know about the Maine mass shooting victims
"His expertise with firearms is going to factor in. I don't think it will change much significantly as to how they will approach this manhunt. Any active shooter is presumed to be an expert in firearms and armed and dangerous, you're always going to assume the worst," said Klaver.
The active manhunt reminds Klaver of the hunt for convicted cop killer Eric Frein, who murdered one Pennsylvania state trooper and wounded another. He hid in the Pennsylvania woods for weeks.
Ongoing manhunt for person-of-interest in Maine shooting
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"Eric Frein was well versed in survival skills. He knew how to handle weapons. He was a hunter, so I think it's similar to that. It's difficult in wooden open terrain," said the former FBI agent.
Officials reported Card had mental health issues, including reports he heard voices, and he threatened to shoot up the military base where he was stationed.
"They'll going to try to talk to any counselors or therapists or doctors he dealt with, and the behavioral unit will try and predict what he does next. Obviously, that's difficult," said Klaver.
Investigators also haven't said what weapon or weapons Card used in the shootings or how he obtained them.
Earlier Thursday near the Card property near Bowdoin, about 15 miles (24 kilometers) from Lewiston, several FBI agents and other heavily armed officers gathered. A military-style vehicle and a white van arrived as a helicopter hovered overhead and someone repeatedly yelled, "FBI! Open the door!" Several loud bangs were heard a short time later.
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A telephone number listed for Card in public records was not in service. A woman who answered a phone number for one of Card's relatives said Thursday afternoon the family was helping the FBI. She didn't give her name or additional details.
The Canada Border Services Agency issued an "armed and dangerous" alert to its officers stationed along the Canada-U.S. border.
Maine Gov. Janet Mills promised to do whatever was needed to find Card and to "hold whoever is responsible for this atrocity accountable ... and to seek full justice for the victims and their families."
Eight murder warrants were issued for Card after authorities identified eight of the victims, police said. Ten more will likely be issued once the names of the rest of the dead are confirmed, said Maine State Police Col. William Ross.
Three of the 13 people wounded in the shootings were in critical condition and five were hospitalized but stable, Central Maine Medical Center officials said.
The attack started at Just-In-Time Recreation, where a children's bowling league was taking place, just before 7 p.m. Wednesday. One bowler, who identified himself only as Brandon, said he heard about 10 shots, thinking the first was a balloon popping.
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"I had my back turned to the door. And as soon as I turned and saw it was not a balloon - he was holding a weapon - I just booked it," he told the AP.
Brandon said he scrambled down the length of the alley, sliding into the pin area and climbing up to hide in the machinery.
Less than 15 minutes after the shooting began, numerous 911 calls started coming in from Schemengees, which was offering 25% discounts to customers who work in the bar or restaurant industry.
Patrick Poulin was supposed to be at the bowling center with his 15-year-old son, who is in a league that was practicing Wednesday. They stayed home, but he estimates there were probably several dozen young bowlers, ages 4 to 18, along with their parents, in the facility. Poulin's brother was there, he said, and shepherded some of the children outside when the shooting began.
"He's pretty shook up," Poulin said Thursday. "And it's just sinking in today, like, wow, I was very close to being there. And a lot of the people that got hurt, I know."
Authorities launched a multistate search for Card on land and water. The Coast Guard sent out a patrol boat Thursday morning along the Kennebec River, but after hours of searching, they found "nothing out of the ordinary," said Chief Petty Officer Ryan Smith, who is in charge of the Coast Guard's Boothbay Harbor Station.
A car believed to belong to Card had been discovered by a boat launch in the town of Lisbon near the Androscoggin River, which connects to the Kennebec, and Card's 15-foot boat remains unaccounted for, Smith said.
A bulletin sent to police across the country after the attack said Card had been committed to a mental health facility for two weeks this past summer after "hearing voices and threats to shoot up" a military base.
A U.S. official said Card was assigned to support training with the Army Reserve's 3rd Battalion, 304th Infantry Regiment in West Point, New York, when commanders became concerned about him.
State police took Card to the Keller Army Community Hospital at West Point for evaluation, according to the official, who was not authorized to publicly discuss the information and spoke to The Associated Press on condition of anonymity.
Immediately after the shooting, police armed with rifles took positions around Lewiston, Maine's second largest city, with a population of 37,000. The once overwhelmingly white mill community has become one of the most diverse cities in northern New England after a major influx of immigrants, mostly from Somalia, in recent years.
The shootings mark the 36th mass killing in the United States this year, according to a database maintained by The Associated Press and USA Today in partnership with Northeastern University.
The Associated Press contributed to this report.