Bryan Grassie, the 18-year-old suspect charged in an East Wareham double-stabbing on July 29, pleaded not guilty to a murder charge in Wareham District Court on Monday.

Grassie was ordered held without bail. A probable cause hearing for Grassie will be held on September 11.

One of the two victims in the stabbing, 18-year-old Bridgewater resident Brendon J. Mahoney, died at Rhode Island Hospital at approximately 4 a.m. on Tuesday, July 31, according to Wareham Police.

An autopsy performed on Mahoney "determined that the cause of death was multiple stab wounds and that the manner of death was homicide," according to a police press release.

Grassie, of 16 Bartlett Lane in East Wareham, was originally charged with two counts of assault with attempt to murder. He was also charged with two counts of assault and battery with a dangerous weapon.

On August 3, Grassie was additionally charged with murder. The original charges still stand, said the prosecutor in the case, Assistant District Attorney Tara Cappola.

The second victim involved in the stabbing incident, Mahoney's brother, 19-year-old Brian P. Mahoney, also suffered multiple stab wounds from the incident. His current condition could not immediately be confirmed.

According to witness testimony found in an affidavit filed by the State Police, a graduation party was being held at a house on Priscilla Avenue when Grassie showed up uninvited.

Grassie exhibited belligerent behavior towards the guests as soon as he arrived, according to witness testimony. Testimony also indicated that Grassie was drunk and slurring his words.

Grassie admitted to being drunk and attending an earlier party, according to the testimony. It is unclear whether alcohol was served at the graduation party.

The parent of a witness to the party told Wareham Week that throughout the night, the owner of the property came in and out of the home to check on the party. The parent believed the owner was sleeping at the time of the stabbing.

During one incident, Grassie was reportedly asked by Brian Mahoney "what his problem was," according to witness testimony in the affidavit. Grassie replied, "If you have a problem, let's take it outside. The street's right there," the witness said.

The verbal exchange between the two continued and Grassie was asked to leave the party repeatedly. Later during the party, Brian Mahoney grabbed Grassie's face and pushed him, according to witness testimony.

A witness was eventually able to get Grassie outside. When outside, Grassie shouted obscene insults toward the Mahoneys, according to witness testimony.

The Mahoneys and two others then ran after Grassie as he went down Priscilla Avenue, according to witness testimony. Brian Mahoney pushed Grassie against a chain link fence and Brendan Mahoney tackled Grassie, according to a witness's testimony.

The fight ensued between Grassie and the Mahoneys, and Grassie stabbed the victims multiple times, according to the report.

Brian Mahoney said in his testimony that he did not realize he was stabbed until he saw blood on his brother and himself. The two ran away once they realized that Grassie had a knife, he said.