Investigators found a note at the home of mass shooting suspect Robert Card, law enforcement sources familiar with the case told ABC News.

The sources declined to describe the contents of the note, its length or its relevance to the investigation.

Investigators recovered a gun from the abandoned car of mass shooting suspect Robert Card, multiple law enforcement sources told ABC News.

Card's white Subaru was found Wednesday night.

Authorities are testing and tracing the gun to determine if it was involved in the shooting, according to multiple law enforcement sources.

Card may have access to other firearms. Sources said law enforcement is treating him as though he is armed and dangerous.

-ABC News' Luke Barr

The shooting unfolded in part during youth night at a local bowling alley. Witnesses described a desperate scene where people hid behind benches and tables and even inside the bowling pin machine at the end of a lane.

Meghan Hutchinson, who was at the bowling alley with her daughter said, "When I turned around, I saw the shooter. ... I don't know if that was just a warning shot or if he shot somebody with that [bullet]."

"Between the lanes there's some swinging doors where they keep all the mechanical stuff out back, so we kind of all just ran that way," she said. "We barricaded in there and another parent was in the room with me. She had a phone, she called 911."

Her daughter, 10-year-old Zoey Levesque, was grazed by a bullet.

"I never thought I'd grow up and get a bullet in my leg," she said. "Like, why do people do this? I was more worried about, like, am I going to live and going to make it out of here? Like, what's going to happen? Are the cops going to come?"

The family of mass shooting suspect Robert Card is cooperating with authorities, law enforcement officials briefed on the investigation told ABC News.

The family is laying out an account of a deeply troubled person, the sources said, bolstering earlier accounts of mental health treatment, voices in his head and alleged threats to shoot up a National Guard facility.

Card's sister told investigators she thought Card might have been looking for an ex-girlfriend at the shooting locations: a bowling alley and a bar, the sources said.

At least 16 people are believed to be dead, though that number is in flux, and dozens more have been injured after a bowling alley came under fire in Lewiston, Maine, Wednesday evening -- the deadliest shooting of the year and one of the deadliest in recent decades.

Riley Dumont said she heard a loud bang after which her father, a retired cop, corralled them into a corner and put protection in front of them including "tables and a big bench that the kids were hiding behind."

“I was laying on top of my daughter. My mother was laying on top of me,” said Dumont. "It felt like it lasted a lifetime," she added. "I just remember people sobbing and crying."

Another witness at the bowling alley, whose name is Brandon, but whose last name was not made available, described hearing a "loud pop."

"Thought it was a balloon," Brandon said. "I had my back turned to the door. As soon as I turned and saw that it was not a balloon, he was holding a weapon. I just bucked it down the lane and I slid basically into where the pins are and climbed up to the machine and was on top of the machines for about 10 minutes until the cops got there."

Meghan Hutchinson, another shooting witness, said, "We were very scared and we didn't know, like, we didn't know what to do, what to expect from this. You know, nothing like this has ever happened here before. We barricaded in there and another parent was in the room with me. She had a phone and she called 911."

Zoe Levesque, 10, was grazed by a bullet.

“I never thought I'd grow up and get a bullet in my leg," said Levesque. "Like, why do people do this? I was more worried about, like, am I going to live and going to make it out of here? Like, what's going to happen? Are the cops going to come?"