PLATTSBURGH — While patrolling along the Rio Grande last May, Ramon Vargas Jr. had no idea he was about to encounter an international murder suspect.

The senior Border Patrol agent was responding to a sensor activation along the Texas river’s bank May 15, 2007, when he spotted a man walking near the water and nearby Mexican border.

“I drove up to the subject and identified myself as a Border Patrol agent,” Vargas testified Wednesday morning during the seventh day of Glen Race’s murder trial in Clinton County Court.

After asking the man for identification, Vargas said, the seemingly friendly traveler pulled out a Nova Scotia ID card bearing the name of Glen Douglas Race, who he recognized as the prime suspect in the murders of 35-year-old Darcy Manor of Mooers Forks and two Canadian men.

To confirm the traveler’s identity, Vargas said, he asked him for a passport.

But when the man reached into one of his two bags, Vargas said, “that’s when I saw what appeared to be the stock of a rifle.”

The situation quickly escalated into a tense and physical confrontation after the agent spotted the weapon, which an expert has linked to the May 10, 2007, shooting death of Manor, a father and volunteer firefighter.

“He immediately went for my service weapon and tackled me,” Vargas told Judge Kevin Ryan as Race bowed his head and stared at the defense table.

“He just went from being real polite to real aggressive.”

Vargas said they were struggling when Race “went for my face, and he bit the left side of my face.”

The Border Patrol agent said he pushed him away, and Race bit his hand.

“After that, I was able to get him down on the ground,” he told District Attorney Andrew Wylie.

“I just said, ‘Don’t move, or I’m going to kill you.’ He immediately froze and didn’t move.”

Other Texas-based Border Patrol agents later took the stand and testified about responding to Vargas’s distress call and about taking the murder suspect into custody about five days after he allegedly killed Manor, hid his body and fled to the southern border in Manor’s truck.

Agent Orlando Castilla said he tried to handcuff the 27-year-old Canadian man but was met with resistance.