A woman who tipped off police that a Cambridge, Massachusetts, man was planning a mass shooting says she now fears for her life.

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Amanda Greenfield told Boston 25 News that she is nervous her roommate, Brian Schwartztrauber, will return to their apartment if he makes bail.

The 54-year-old Schwartztrauber is accused of buying ammunition illegally at a local gun show, which he had allegedly planned to use for a mass shooting. He was held on $25,000 cash bail following his arraignment in Cambridge District Court on Wednesday.

"I couldn’t get the words that he was saying out of my head. I didn’t want to wait on it. It seemed imminent, the way he said, 'I can’t wait for my sniper rifle to get here,'" said Greenfield.

She said she overheard a disturbing conversation.

"To say nothing and allow dozens of people to die or be murdered, I think that’s disgusting," Greenfield said.

She is confident Schwartztrauber will post bail, but she said she doesn't regret the choice she made.

"I firmly believe that people would have died if I remained silent.One hundred percent yes," Greenfield said.

Judge Roanne Sragow ordered that Schwartztrauber be released with a GPS monitoring device, remain in Massachusetts, not consume any alcohol, comply with alcohol monitoring, consume no drugs without a prescription, not possess any weapons or ammunition and not attend any gun shows or gun stores where firearms are sold.

He was also ordered to have no contact with the witness and to abide by a restraining order. A not guilty plea was entered on his behalf.

Prosecutors say Schwartztrauber's roommate overhead concerning language about Schwartztrauber's presence at a gun show and reported it to police.

Middlesex County District Attorney Marian Ryan said during a news conference Thursday that Schwartztrauber will face additional charges out of Wilmington.

On March 2, Wilmington police responded to Shriners Auditorium for a report of a disruptive patron at the Northeast Gun Show.

Officers allegedly found Schwarztrauber, who was being disruptive and refused to leave the show.

When police approached Schwartztrauber, they also allegedly detected a strong odor of alcohol. While police were speaking to him, they heard from Cambridge police concerning statements allegedly made by Schwartztrauber indicating that he was going to use a firearm and ammunition to allegedly conduct a shooting spree.

Schwartztrauber was placed into protective custody. Police later learned that Schwarztrauber had allegedly purchased ammunition at the gun show without a firearms identification card.

Police then located three 50-round boxes of PPU Handgun Line 9 mm Luger ammunition in Schwartztrauber's vehicle. Schwartztrauber was arrested and charged with possessing ammunition without an FID card.

Cambridge police subsequently obtained a search warrant for Schwartztrauber's home in Cambridge on March 3, where they allegedly found a box of Hornady Valkyrie 224 rifle ammunition. No firearms were located. Cambridge police charged Schwartztrauber with possession of ammunition without a license.

Police located the vendor, Stephen Fowler, 69, of Guilford, Connecticut, on March 2 and charged him after an investigation into the sale of the ammunition on March 3.

Fowler was charged with selling ammunition without complying with the requirements relating to firearms identifications cards. He was arraigned in Woburn District Court on March 5. Judge William Martin released Fowler on $500 cash bail and ordered him not to sell firearms or ammunition in Massachusetts. Fowler is due back in court May 22.

Schwartztrauber is expected to be arraigned in Woburn District Court on the charges out of Wilmington at a later date.

Schwartztrauber is due back in Cambridge District Court on April 2.