Police have a suspect in custody for the shooting that shut down Dartmouth-Hitchcock Medical Center for hours Tuesday.

Authorities say Travis Frink, 49, of Rhode Island, has been arrested for the first-degree murder of his mother. Pamela Ferriere, 70, of Groton, New Hampshire, was staying in the hospital’s ICU. New Hampshire Attorney General Gordon MacDonald tells us Frink signed in at the hospital’s visitor's desk at around 1:15 p.m. Less than 10 minutes later, police got calls that shots were fired.

"The facts gathered to this point reveal that the purpose of Mr. Frink’s visit to the hospital today was to kill his mother," said MacDonald. "More than one shot was fired."

Police say the crime scene is still under investigation, but no one else was injured. They didn't take any questions Tuesday night, so we still don't know anything about motive.

Authorities expect Frink to be arraigned at Grafton County Superior Court Wednesday.

Multiple hospital workers told us it was one of the scariest days of their lives. We talked to them and patients as they waited outside, for more than three hours.

"I was pretty scared, so I had to pray two times for everyone," said Colton Ricottelli, who was evacuated.

The little boy was headed to the ear doctor when chaos erupted.

"Someone came into the room to tell us to evacuate, come outside, then they kept telling us to move farther and farther," Ricotelli explained.

Mike Carey was bringing his 86-year old father to get an X-ray. He said the unknown was unsettling.

"They said we've got to go," said Carey. "They had us run from this parking lot into the buildings."

The workers were just as terrified. Rhiannon Houghton says she saw the "code silver" notification show up on her computer, indicating there was an active shooter, and it was one of the scariest moments of her life.

"The only patients that were inside were the ones who were in the middle of procedures and they were locked behind closed doors," said Houghton.

She says at one point, people just yelled "Run!"

"We just ran, we hid and then we were hiding inside," said Houghton.

"We heard a lot of sirens; we knew there were a lot of vehicles coming," said Bridget Logan, a nurse practitioner.

Hospital staff handed out water bottles as patients sat outside waiting to get back into the main building. Logan was shaken up but relieved no one else was hurt.

"It definitely shakes you, and makes you think about where your kids are and how your co-workers are and it makes you think about the work we do every day at a hospital," said Logan.

The Dartmouth Hitchcock CEO said she believes the medical center’s weeks of active-shooter training helped keep the situation under control.